XWiki Rendering is vulnerable to XSS attacks through insecure XHTML syntax

Vulnerability Description

XWiki Rendering is a generic rendering system that converts textual input in a given syntax (wiki syntax, HTML, etc) into another syntax (XHTML, etc). Starting in version 5.4.5 and prior to version 14.10, the XHTML syntax depended on the `xdom+xml/current` syntax which allows the creation of raw blocks that permit the insertion of arbitrary HTML content including JavaScript. This allows XSS attacks for users who can edit a document like their user profile (enabled by default). This has been fixed in version 14.10 by removing the dependency on the `xdom+xml/current` syntax from the XHTML syntax. Note that the `xdom+xml` syntax is still vulnerable to this attack. As it's main purpose is testing and its use is quite difficult, this syntax shouldn't be installed or used on a regular wiki. There are no known workarounds apart from upgrading.

References

• https://github.com/xwiki/xwiki-rendering/security/advisories/GHSA-w3wh-g4m9-783p
• https://github.com/xwiki/xwiki-rendering/commit/a4ca31f99f524b9456c64150d6f375984aa81ea7
• https://jira.xwiki.org/browse/XRENDERING-660