CVE 2011-2979
Bugzilla 4.1.x before 4.1.3 generates different responses for certain assignee queries depending on whether the group name is valid, which allows remote attackers to determine the existence of private group names via a custom search. NOTE: this vulnerability exists because of a CVE-2010-2756 regression.
See the 
CVE page on Mitre.org
for more details.
