Disabling a user account changes its author, allowing RCE from user account in XWiki

XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. When an admin disables a user account, the user's profile is executed with the admin's rights. This allows a user to place malicious code in the user profile before getting an admin to disable the user account. To reproduce, as a user without script nor programming rights, edit the about section of your user profile and add {{groovy}}services.logging.getLogger("attacker").error("Hello from Groovy!"){{/groovy}}.
As an admin, go to the user profile and click the "Disable this account" button. Then, reload the page. If the logs show attacker - Hello from Groovy! then the instance is vulnerable. This has been patched in XWiki 14.10.21, 15.5.5, 15.10.6 and 16.0.0. Users are advised to upgrade. There are no known workarounds for this vulnerability.

Workarounds

We're not aware of any workaround except upgrading.

References

• https://jira.xwiki.org/browse/XWIKI-21611
• https://github.com/xwiki/xwiki-platform/commit/f89c8f47fad6e5cc7e68c69a7e0acde07f5eed5a