Problem

Due to an encoding issue in the serialization layer, malicious markup nested in a noscript element was not encoded correctly. noscript is disabled in the default configuration, but might have been enabled in custom scenarios. This allows bypassing the cross-site scripting mechanism of typo3/html-sanitizer.

Solution

Update to typo3/html-sanitizer versions 1.5.1 or 2.1.2 that fix the problem described.

Credits

Thanks to David Klein and Yaniv Nizry who reported this issue, and to TYPO3 security team members Oliver Hader and Benjamin Franzke who fixed the issue.

References