CVSS: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N/E:F/RL:O/RC:C (5.7)

Problem

Due to a parsing issue in the upstream package masterminds/html5, malicious markup used in a sequence with special HTML CDATA sections cannot be filtered and sanitized. This allows bypassing the cross-site scripting mechanism of typo3/html-sanitizer.

Besides that, the upstream package masterminds/html5 provides HTML raw text elements (script, style, noframes, noembed and iframe) as DOMText nodes, which were not processed and sanitized further. None of the mentioned elements were defined in the default builder configuration, that's why only custom behaviors, using one of those tag names, were vulnerable to cross-site scripting.

Solution

Update to typo3/html-sanitizer versions 1.5.0 or 2.1.1 that fix the problem described.

Credits

Thanks to David Klein who reported this issue, and to TYPO3 security team member Oliver Hader who fixed the issue.