Last modified: 2013-04-22 16:14:17 UTC
Currently MediaWiki software has "UserRights" hook (http://www.mediawiki.org/wiki/Manual:Hooks/UserRights) to processing some data AFTER save groups changes to database. Please add new hook to processing data before changes (i. e. to abort changes with extension function).
https://gerrit.wikimedia.org/r/27266
(In reply to comment #1) > https://gerrit.wikimedia.org/r/27266 Status Abandoned
Since MW 1.18, there are the UserAddGroup and UserRemoveGroup hooks. Unless the reporter has some special requirement that needs a hook specifically in the Special:Userrights page, those fulfill the necessary functionality.