parse.c in sudo 1.6.9p17 through 1.6.9p19 does not properly interpret a system group (aka %group) in the sudoers file during authorization decisions for a user who belongs to that group, which allows local users to leverage an applicable sudoers file and gain root privileges via a sudo command.
https://bugzilla.novell.com/show_bug.cgi?id=468923
http://www.vupen.com/english/advisories/2009/1865
http://www.vmware.com/security/advisories/VMSA-2009-0009.html
http://www.redhat.com/support/errata/RHSA-2009-0267.html
http://www.gratisoft.us/bugzilla/show_bug.cgi?id=327
http://secunia.com/advisories/35766
http://secunia.com/advisories/33885