TemplateInjection.qhelp

<!DOCTYPE qhelp SYSTEM "qhelp.dtd">
<qhelp>
    <overview>
        <p>
                A template from a server templating engine such as Jinja constructed from user input can allow the user to execute arbitrary code using certain template features. It can also allow for cross-site scripting.
        </p>
    </overview>
    <recommendation>
        <p>
            Ensure that an untrusted value is not used to directly construct a template. 
            Jinja also provides <code>SandboxedEnvironment</code> that prohibits access to unsafe methods and attributes. This can be used if constructing a template from user input is absolutely necessary. 
        </p>
    </recommendation>
    <example>
        <p>In the following case, <code>template</code> is used to generate a Jinja2 template string. This can lead to remote code execution. </p>
        <sample src="examples/JinjaBad.py" />

        <p>The following is an example of a string that could be used to cause remote code execution when interpreted as a template:</p>
        <sample src="examples/template_exploit.txt" />

        <p>In the following case, user input is not used to construct the template. Instead, it is only used as the parameters to render the template, which is safe.</p>
        <sample src="examples/JinjaGoodParam.py" />
        
        <p>In the following case, a <code>SandboxedEnvironment</code> is used, preventing remote code execution.</p>
        <sample src="examples/JinjaGoodSandbox.py" />
    </example>
    <references>
        <li>Portswigger: <a href="https://portswigger.net/web-security/server-side-template-injection">Server-Side Template Injection</a>.</li>
    </references>
</qhelp>