The Xss::filter() method does not remove srcdoc attributes from iframe tags.
This attribute can be used to inject JS into the page.
The XSS filter removes other dangerous attributes like onclick or onload, so I think it should also remove srcdoc.
Xss::filter() does not allow iframe tags by default, so it needs to be called explicitly with iframe in the $allowed_html_tags parameter to be vulnerable.
You could argue that this is a misuse of the XSS filter, but I think it is an easy mistake to make and it could benefit from this hardening.
This was originally logged as a private issue to the security team, but was cleared to be moved to the public queue.
If someone calls this:
\Drupal\Component\Utility\Xss::filter('<iframe srcdoc="<script>alert(document.cookie)</script>"></iframe>', ['iframe'])
They could expect a safe iframe tag to be returned but instead the returned HTML could containe malicious JS.
Remove srcdoc attributes in Xss::attributes().
Active
11.0 🔥
other
It makes Drupal less vulnerable to abuse or misuse. Note, this is the preferred tag, though the Security tag has a large body of issues tagged to it. Do NOT publicly disclose security vulnerabilities; contact the security team instead. Anyone (whether security team or not) can apply this tag to security improvements that do not directly present a vulnerability e.g. hardening an API to add filtering to reduce a common mistake in contributed modules.
Reading up on srcdoc on https://developer.mozilla.org/en-US/docs/Web/API/HTMLIFrameElement/srcdoc and the example
iframe.srcdoc = `<!doctype html><p>Hello World!</p>`;
document.body.appendChild(iframe);
Shows HTML being used so would agree it probably should be stripped. Not sure if this needs a CR? Will let committer decide