XWiki Platform is a generic wiki platform. Starting in version 3.0.1 and prior to versions 4.10.19, 15.5.4, and 15.10-rc-1, the HTML escaping of escaping tool that is used in XWiki doesn't escape `{`, which, when used in certain places, allows XWiki syntax injection and thereby remote code execution. The vulnerability has been fixed in XWiki 14.10.19, 15.5.5, and 15.9 RC1. Apart from upgrading, there is no generic workaround. However, replacing `$escapetool.html` by `$escapetool.xml` in XWiki documents fixes the vulnerability. In a standard XWiki installation, the maintainers are only aware of the document `Panels.PanelLayoutUpdate` that exposes this vulnerability, patching this document is thus a workaround. Any extension could expose this vulnerability and might thus require patching, too.
https://jira.xwiki.org/browse/XWIKI-21438
https://jira.xwiki.org/browse/XCOMMONS-2828
https://github.com/xwiki/xwiki-commons/security/advisories/GHSA-hf43-47q4-fhq5
https://github.com/xwiki/xwiki-commons/commit/ed7ff515a2436a1c6dcbd0c6ca0c41e434d58915
https://github.com/xwiki/xwiki-commons/commit/b94142e2a66ec32e89eacab67c3da8d91f5ef93a
https://github.com/xwiki/xwiki-commons/commit/b0805160ec7b01ee12417e79cb384e60ae4817aa