XWiki Realtime WYSIWYG Editor extension allows privilege escalation (PR) through realtime WYSIWYG editing

Impact

NOTE: The Realtime WYSIWYG Editor extension was experimental, and thus not recommended, in the versions affected by this vulnerability. It has become enabled by default, and thus recommended, starting with XWiki 16.9.0.

A user with only edit right can join a realtime editing session where others, that where already there or that may join later, have script or programming access rights. This user can then insert script rendering macros that are executed for those users in the realtime session that have script or programming rights. The inserted scripts can be used to gain more access rights.

Here's an example that works with XWiki 15.10.9+ and 16.2.0+:

• the attacker starts editing a wiki page in realtime (for which they have edit right)
• another user, with script or programming access right joins the editing session (e.g. by clicking on a link / URL provided by the attacker)
• the attacker inserts a script rendering macro, say {{velocity}}I can run scripts{{/velocity}}, in the edited content, using the WYSIWYG editor UI
• the edited content is reloaded for both the attacker and the other user, in order to render the inserted macro
  • the attacker gets a rendering error message
  • the other user sees "I can run scripts"

The attacker can obviously use more advanced scripts to gain access rights.

Before XWiki 15.10.9 and 16.2.0 the edited content was not re-rendered for all the users in the editing sesesion, but only for the user that inserted the macro. This means that in order to reproduce the problem the other user had to insert or update a macro or save and view the content.

Patches

This vulnerability has been patched in XWiki 15.10.12, 16.4.1 and 16.6.0-rc-1.

Workarounds

To avoid this vulnerability you can:

• either disable the realtime WYSIWYG editing by disabling the xwiki-realtime CKEditor plugin from the WYSIWYG editor administration section
• or uninstall the Realtime WYSIWYG Editor extension (org.xwiki.platform:xwiki-platform-realtime-wysiwyg-ui)