thumb.php in MediaWiki before 1.15.2, when used with access-restriction mechanisms such as img_auth.php, does not check user permissions before providing scaled images, which allows remote attackers to bypass intended access restrictions and read private images via unspecified manipulations.
http://www.vupen.com/english/advisories/2010/1001
http://www.vupen.com/english/advisories/2010/0685
http://www.debian.org/security/2010/dsa-2022
http://svn.wikimedia.org/svnroot/mediawiki/tags/REL1_15_2/phase3/RELEASE-NOTES
http://secunia.com/advisories/39656
http://secunia.com/advisories/39022
http://lists.wikimedia.org/pipermail/mediawiki-announce/2010-March/000088.html
http://lists.opensuse.org/opensuse-security-announce/2010-04/msg00006.html