XWiki Commons missing escaping of `{` in Velocity escapetool allows remote code execution

Impact

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.

To reproduce in an XWiki installation, open <xwiki-host>/xwiki/bin/view/Panels/PanelLayoutUpdate?place=%7B%7B%2Fhtml%7D%7D%7B%7Basync%20async%3Dfalse%7D%7D%7B%7Bvelocity%7D%7D%23evaluate(%24request.eval)%7B%7B%2Fvelocity%7D%7D%7B%7B%2Fasync%7D%7D&eval=Hello%20from%20URL%20Parameter!%20I%20got%20programming%3A%20%24services.security.authorization.hasAccess(%27programming%27) where <xwiki-host> is the URL of your XWiki installation. If this displays You are not admin on this place Hello from URL Parameter! I got programming: true, the installation is vulnerable.

Patches

The vulnerability has been fixed on XWiki 14.10.19, 15.5.5, and 15.9 RC1.

Workarounds

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, we're 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.

References

• https://github.com/xwiki/xwiki-commons/commit/b94142e2a66ec32e89eacab67c3da8d91f5ef93a
• https://jira.xwiki.org/browse/XCOMMONS-2828
• https://jira.xwiki.org/browse/XWIKI-21438