TYPO3 is an open source PHP based web content management system released under the GNU GPL. In affected versions DOM processing instructions are not handled correctly. This allows bypassing the cross-site scripting mechanism of typo3/html-sanitizer. This vulnerability has been addressed in versions 1.5.3 and 2.1.4. Users are advised to upgrade. There are no known workarounds for this vulnerability.

TYPO3 HTML Sanitizer is an HTML sanitizer, written in PHP, aiming to provide cross-site-scripting-safe markup based on explicitly allowed tags, attributes and values. Starting in version 1.0.0 and prior to versions 1.5.1 and 2.1.2, 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. Versions 1.5.1 and 2.1.2 fix the problem.

HTML sanitizer is written in PHP, aiming to provide XSS-safe markup based on explicitly allowed tags, attributes and values. In versions prior to 1.5.0 or 2.1.1, malicious markup used in a sequence with special HTML CDATA sections cannot be filtered and sanitized due to a parsing issue in the upstream package masterminds/html5. This allows bypassing the cross-site scripting mechanism of typo3/html-sanitizer. 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. This issue has been fixed in versions 1.5.0 and 2.1.1.

The typo3/html-sanitizer package is an HTML sanitizer, written in PHP, aiming to provide XSS-safe markup based on explicitly allowed tags, attributes and values. Due to a parsing issue in the upstream package `masterminds/html5`, malicious markup used in a sequence with special HTML comments cannot be filtered and sanitized. This allows for a bypass of the cross-site scripting mechanism of `typo3/html-sanitizer`. This issue has been addressed in versions 1.0.7 and 2.0.16 of the `typo3/html-sanitizer` package. Users are advised to upgrade. There are no known workarounds for this issue.