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68 lines
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Exploit Requirements</a><li class="nav-list-item active"><a href="#" class="nav-list-expander"><svg viewBox="0 0 24 24"><use xlink:href="#svg-arrow-right"></use></svg></a><a href="/docs/using-metasploit/other/oracle-support/" class="nav-list-link">Oracle Support</a><ul class="nav-list"><li class="nav-list-item active"><a href="/docs/using-metasploit/other/oracle-support/how-to-get-oracle-support-working-with-kali-linux.html" class="nav-list-link">How to get Oracle Support working with Kali Linux</a><li class="nav-list-item active"><a href="/docs/using-metasploit/other/oracle-support/oracle-usage.html" class="nav-list-link">Oracle Usage</a></ul><li class="nav-list-item active"><a href="/docs/using-metasploit/other/why-cve-is-not-available.html" class="nav-list-link">Why CVE is not available</a></ul></ul><li class="nav-list-item active"><a href="#" class="nav-list-expander"><svg viewBox="0 0 24 24"><use xlink:href="#svg-arrow-right"></use></svg></a><a href="/docs/development/" 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role="main"><p>In Metasploit, exploits and auxiliary modules support the check command that allows the user to be able to determine the vulnerable state before using the module. This feature is handy for those who need to verify the vulnerability without actually popping a shell, and used to quickly identify all vulnerable, or possibly exploitable machines on the network.</p><p>Although vulnerability checks aren’t the focus of Metasploit, because it isn’t a vulnerability scanner like Nexpose, we do actually encourage people to implement the check() method anyway to add more value to the module. If you do write one, make sure to keep these guidelines in mind:</p><h2 id="check-method-output"> <a href="#check-method-output" class="anchor-heading" aria-labelledby="check-method-output"><svg viewBox="0 0 16 16" aria-hidden="true"><use xlink:href="#svg-link"></use></svg></a> Check Method Output</h2><p>Modules messages are important to the user, because they keep the user informed about what the module is doing, and usually make the module more debuggable. However, you do also want to keep your messages in verbose mode because it becomes really noisy if the check is used against multiple targets. Ideally, you only should be using these print methods:</p><div class="table-wrapper"><table><thead><tr><th>Method<th>Description<tbody><tr><td><strong>vprint_line()</strong><td>verbose version of print_line<tr><td><strong>vprint_status()</strong><td>verbose version of print_status that begins with “[*]”<tr><td><strong>vprint_error()</strong><td>verbose version of print_error that begins with “[x]”<tr><td><strong>vprint_warning()</strong><td>verbose version of print_warning that begins with “[!]”, in yellow</table></div><p>Better yet, use the <code class="language-plaintext highlighter-rouge">CheckCode</code> description to provide additional information (see below).</p><p>Note: You shouldn’t be printing if a target is vulnerable or not, as this is automatically handled by the framework when your method returns a check code.</p><h2 id="check-codes"> <a href="#check-codes" class="anchor-heading" aria-labelledby="check-codes"><svg viewBox="0 0 16 16" aria-hidden="true"><use xlink:href="#svg-link"></use></svg></a> Check Codes</h2><p>Once you have determined the vulnerable state, you should return a check code. Check codes are constants defined in <code class="language-plaintext highlighter-rouge">Msf::Exploit::CheckCode</code>, and these are the ones you can use:</p><div class="table-wrapper"><table><thead><tr><th>Checkcode<th>Description<tbody><tr><td><strong>Exploit::CheckCode::Unknown</strong><td>Used if the module fails to retrieve enough information from the target machine, such as due to a timeout.<tr><td><strong>Exploit::CheckCode::Safe</strong><td>Used if the check fails to trigger the vulnerability, or even detect the service.<tr><td><strong>Exploit::CheckCode::Detected</strong><td>The target is running the service in question, but the check fails to determine whether the target is vulnerable or not.<tr><td><strong>Exploit::CheckCode::Appears</strong><td>This is used if the vulnerability is determined based on passive reconnaissance. For example: version, banner grabbing, or simply having the resource that’s known to be vulnerable.<tr><td><strong>Exploit::CheckCode::Vulnerable</strong><td>Only used if the check is able to actually take advantage of the bug, and obtain some sort of hard evidence. For example: for a command execution type bug, get a command output from the target system. For a directory traversal, read a file from the target, etc. Since this level of check is pretty aggressive in nature, you should not try to DoS the host as a way to prove the vulnerability.<tr><td><strong>Exploit::CheckCode::Unsupported</strong><td>The exploit does not support the check method. If this is the case, then you don’t really have to add the check method.</table></div><p>The <code class="language-plaintext highlighter-rouge">CheckCode</code> also supports an optional description which is printed by the framework upon completion of the <code class="language-plaintext highlighter-rouge">check</code> method. For example:</p><div class="language-ruby highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">return</span> <span class="no">CheckCode</span><span class="o">::</span><span class="no">Appears</span><span class="p">(</span><span class="s1">'Vulnerable component XYZ is installed'</span><span class="p">)</span>
|
||
</code></pre></div></div><p><code class="language-plaintext highlighter-rouge">MetasploitModule#check</code> methods should capture any known <code class="language-plaintext highlighter-rouge">raise</code> from methods called and return value of class <code class="language-plaintext highlighter-rouge">Msf::Exploit::CheckCode</code>. Basically, that means avoiding the use of <code class="language-plaintext highlighter-rouge">fail_with</code> or raising exceptions that are not handled within the check method.</p><h2 id="remote-check-example"> <a href="#remote-check-example" class="anchor-heading" aria-labelledby="remote-check-example"><svg viewBox="0 0 16 16" aria-hidden="true"><use xlink:href="#svg-link"></use></svg></a> Remote Check Example</h2><p>Here’s an abstract example of how a Metasploit check might be written:</p><div class="language-ruby highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1">#</span>
|
||
<span class="c1"># Returns a check code that indicates the vulnerable state on an app running on OS X</span>
|
||
<span class="c1">#</span>
|
||
<span class="k">def</span> <span class="nf">check</span>
|
||
<span class="k">if</span> <span class="n">exec_cmd_via_http</span><span class="p">(</span><span class="s2">"id"</span><span class="p">)</span> <span class="o">=~</span> <span class="sr">/uid=\d+\(.+\)/</span>
|
||
<span class="c1"># Found the correct ID output, good indicating our command executed</span>
|
||
<span class="k">return</span> <span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Vulnerable</span>
|
||
<span class="k">end</span>
|
||
|
||
<span class="n">http_body</span> <span class="o">=</span> <span class="n">get_http_body</span>
|
||
<span class="k">if</span> <span class="n">http_body</span>
|
||
<span class="k">if</span> <span class="n">http_body</span> <span class="o">=~</span> <span class="sr">/Something CMS v1\.0/</span>
|
||
<span class="c1"># We are able to find the version therefore more precise about the vuln state</span>
|
||
<span class="k">return</span> <span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Appears</span>
|
||
<span class="k">elsif</span> <span class="n">http_body</span> <span class="o">=~</span> <span class="sr">/Something CMS/</span>
|
||
<span class="c1"># All we can tell the vulnerable app is running, but no more info to</span>
|
||
<span class="c1"># determine the vuln</span>
|
||
<span class="k">return</span> <span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Detected</span>
|
||
<span class="k">end</span>
|
||
<span class="k">else</span>
|
||
<span class="n">vprint_error</span><span class="p">(</span><span class="s2">"Unable to determine due to a HTTP connection timeout"</span><span class="p">)</span>
|
||
<span class="k">return</span> <span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Unknown</span>
|
||
<span class="k">end</span>
|
||
|
||
<span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Safe</span>
|
||
<span class="k">end</span>
|
||
</code></pre></div></div><p>Note: If you are writing an auxiliary module with the <code class="language-plaintext highlighter-rouge">Msf::Auxiliary::Scanner</code> mixin, you should declare your check method like this:</p><div class="language-ruby highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">def</span> <span class="nf">check_host</span><span class="p">(</span><span class="n">ip</span><span class="p">)</span>
|
||
<span class="c1"># Do your thing</span>
|
||
<span class="k">end</span>
|
||
</code></pre></div></div><h3 id="local-exploit-check-example"> <a href="#local-exploit-check-example" class="anchor-heading" aria-labelledby="local-exploit-check-example"><svg viewBox="0 0 16 16" aria-hidden="true"><use xlink:href="#svg-link"></use></svg></a> Local Exploit Check Example</h3><p>Most local exploit checks are done by checking the version of the vulnerable file, which is considered passive, therefore they should be flagging <code class="language-plaintext highlighter-rouge">Exploit::CheckCode::Appears</code>. Passive local exploit checks don’t necessarily mean they are less reliable, in fact, they are not bad. But to qualify for <code class="language-plaintext highlighter-rouge">Exploit::CheckCode::Vulnerable</code>, your check should do the extra mile, which means either you somehow make the program return a vulnerable response, or you inspect the vulnerable code.</p><p>An example of making the program return a vulnerable response is ShellShock (the following is specific for VMWare):</p><div class="language-ruby highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="k">def</span> <span class="nf">check</span>
|
||
<span class="n">check_str</span> <span class="o">=</span> <span class="no">Rex</span><span class="o">::</span><span class="no">Text</span><span class="p">.</span><span class="nf">rand_text_alphanumeric</span><span class="p">(</span><span class="mi">5</span><span class="p">)</span>
|
||
<span class="c1"># ensure they are vulnerable to bash env variable bug</span>
|
||
<span class="k">if</span> <span class="n">cmd_exec</span><span class="p">(</span><span class="s2">"env x='() { :;}; echo </span><span class="si">#{</span><span class="n">check_str</span><span class="si">}</span><span class="s2">' bash -c echo"</span><span class="p">).</span><span class="nf">include?</span><span class="p">(</span><span class="n">check_str</span><span class="p">)</span> <span class="o">&&</span>
|
||
<span class="n">cmd_exec</span><span class="p">(</span><span class="s2">"file '</span><span class="si">#{</span><span class="n">datastore</span><span class="p">[</span><span class="s1">'VMWARE_PATH'</span><span class="p">]</span><span class="si">}</span><span class="s2">'"</span><span class="p">)</span> <span class="o">!~</span> <span class="sr">/cannot open/</span>
|
||
|
||
<span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Vulnerable</span>
|
||
<span class="k">else</span>
|
||
<span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Safe</span>
|
||
<span class="k">end</span>
|
||
<span class="k">end</span>
|
||
</code></pre></div></div><p>One way to inspect the vulnerable code is to come up with a signature, and see if it exists in the vulnerable process. Here’s an example with adobe_sandbox_adobecollabsync.rb:</p><div class="language-ruby highlighter-rouge"><div class="highlight"><pre class="highlight"><code><span class="c1"># 'AdobeCollabSyncTriggerSignature' => "\x56\x68\xBC\x00\x00\x00\xE8\xF5\xFD\xFF\xFF"</span>
|
||
<span class="c1"># 'AdobeCollabSyncTrigger' => 0x18fa0</span>
|
||
|
||
<span class="k">def</span> <span class="nf">check_trigger</span>
|
||
<span class="n">signature</span> <span class="o">=</span> <span class="n">session</span><span class="p">.</span><span class="nf">railgun</span><span class="p">.</span><span class="nf">memread</span><span class="p">(</span><span class="vi">@addresses</span><span class="p">[</span><span class="s1">'AcroRd32.exe'</span><span class="p">]</span> <span class="o">+</span> <span class="n">target</span><span class="p">[</span><span class="s1">'AdobeCollabSyncTrigger'</span><span class="p">],</span> <span class="n">target</span><span class="p">[</span><span class="s1">'AdobeCollabSyncTriggerSignature'</span><span class="p">].</span><span class="nf">length</span><span class="p">)</span>
|
||
<span class="k">if</span> <span class="n">signature</span> <span class="o">==</span> <span class="n">target</span><span class="p">[</span><span class="s1">'AdobeCollabSyncTriggerSignature'</span><span class="p">]</span>
|
||
<span class="k">return</span> <span class="kp">true</span>
|
||
<span class="k">end</span>
|
||
|
||
<span class="k">return</span> <span class="kp">false</span>
|
||
<span class="k">end</span>
|
||
|
||
<span class="k">def</span> <span class="nf">check</span>
|
||
<span class="vi">@addresses</span> <span class="o">=</span> <span class="p">{}</span>
|
||
<span class="n">acrord32</span> <span class="o">=</span> <span class="n">session</span><span class="p">.</span><span class="nf">railgun</span><span class="p">.</span><span class="nf">kernel32</span><span class="o">.</span><span class="no">GetModuleHandleA</span><span class="p">(</span><span class="s2">"AcroRd32.exe"</span><span class="p">)</span>
|
||
<span class="vi">@addresses</span><span class="p">[</span><span class="s1">'AcroRd32.exe'</span><span class="p">]</span> <span class="o">=</span> <span class="n">acrord32</span><span class="p">[</span><span class="s2">"return"</span><span class="p">]</span>
|
||
<span class="k">if</span> <span class="vi">@addresses</span><span class="p">[</span><span class="s1">'AcroRd32.exe'</span><span class="p">]</span> <span class="o">==</span> <span class="mi">0</span>
|
||
<span class="k">return</span> <span class="no">Msf</span><span class="o">::</span><span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Unknown</span>
|
||
<span class="k">elsif</span> <span class="n">check_trigger</span>
|
||
<span class="k">return</span> <span class="no">Msf</span><span class="o">::</span><span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Vulnerable</span>
|
||
<span class="k">else</span>
|
||
<span class="k">return</span> <span class="no">Msf</span><span class="o">::</span><span class="no">Exploit</span><span class="o">::</span><span class="no">CheckCode</span><span class="o">::</span><span class="no">Detected</span>
|
||
<span class="k">end</span>
|
||
<span class="k">end</span>
|
||
</code></pre></div></div><p>Another possible way to inspect is grab the vulnerable file, and use Metasm. But of course, this is a lot slower and generates more network traffic.</p><h2 id="autocheck-mixin"> <a href="#autocheck-mixin" class="anchor-heading" aria-labelledby="autocheck-mixin"><svg viewBox="0 0 16 16" aria-hidden="true"><use xlink:href="#svg-link"></use></svg></a> AutoCheck Mixin</h2><p>Metasploit offers the possibility to automatically call the <code class="language-plaintext highlighter-rouge">check</code> method before the <code class="language-plaintext highlighter-rouge">exploit</code> or <code class="language-plaintext highlighter-rouge">run</code> method is run. Just prepend the <code class="language-plaintext highlighter-rouge">AutoCheck</code> module for this, nothing more:</p><div class="language-ruby highlighter-rouge"><div class="highlight"><pre class="highlight"><code> <span class="n">prepend</span> <span class="no">Msf</span><span class="o">::</span><span class="no">Exploit</span><span class="o">::</span><span class="no">Remote</span><span class="o">::</span><span class="no">AutoCheck</span>
|
||
</code></pre></div></div><p>According to the <code class="language-plaintext highlighter-rouge">CheckCode</code> returned by the <code class="language-plaintext highlighter-rouge">check</code> method, Framework will decided if the module should be executed or not:</p><div class="table-wrapper"><table><thead><tr><th>Checkcode<th>Module executed?<tbody><tr><td><strong>Exploit::CheckCode::Vulnerable</strong><td>yes<tr><td><strong>Exploit::CheckCode::Appears</strong><td>yes<tr><td><strong>Exploit::CheckCode::Detected</strong><td>yes<tr><td><strong>Exploit::CheckCode::Safe</strong><td>no<tr><td><strong>Exploit::CheckCode::Unsupported</strong><td>no<tr><td><strong>Exploit::CheckCode::Unknown</strong><td>no</table></div><p>This mixin brings two new options that let the operator control its behavior:</p><ul><li><code class="language-plaintext highlighter-rouge">AutoCheck</code>: Sets whether or not the <code class="language-plaintext highlighter-rouge">check</code> method will be run. Default is <code class="language-plaintext highlighter-rouge">true</code>.<li><code class="language-plaintext highlighter-rouge">ForceExploit</code>: Override the check result. The <code class="language-plaintext highlighter-rouge">check</code> method is run but the module will be executed regardless of the result. Default is <code class="language-plaintext highlighter-rouge">false</code>.</ul><hr><footer><p><a href="#top" id="back-to-top">Back to top</a></p><p class="text-small text-grey-dk-000 mb-0"> <a href="https://github.com/rapid7/metasploit-framework/tree/master/docs/metasploit-framework.wiki/How-to-write-a-check-method.md" id="edit-this-page">Edit this page on GitHub</a></p></footer></div></div><div class="search-overlay"></div></div><script type="text/javascript" src="/assets/js/toggle_mode.js"></script> <script> var config = { theme: 'default', logLevel: 'fatal', securityLevel: 'strict', startOnLoad: true, arrowMarkerAbsolute: false, er: { diagramPadding: 20, layoutDirection: 'TB', minEntityWidth: 100, minEntityHeight: 75, entityPadding: 15, stroke: 'gray', fill: 'honeydew', fontSize: 12, useMaxWidth: true, }, flowchart:{ diagramPadding: 8, htmlLabels: true, curve: 'basis', }, sequence: { diagramMarginX: 50, diagramMarginY: 10, actorMargin: 50, width: 150, height: 65, boxMargin: 10, boxTextMargin: 5, noteMargin: 10, messageMargin: 35, messageAlign: 'center', mirrorActors: true, bottomMarginAdj: 1, useMaxWidth: true, rightAngles: false, showSequenceNumbers: false, }, gantt: { titleTopMargin: 25, barHeight: 20, barGap: 4, topPadding: 50, leftPadding: 75, fontSize: 11, gridLineStartPadding: 35, fontFamily: '\'Open Sans\', sans-serif', numberSectionStyles: 4, axisFormat: '%Y-%m-%d', topAxis: false, }, }; mermaid.initialize(config); window.mermaid.init(undefined, document.querySelectorAll('.language-mermaid')); </script>
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