Integer overflow in the vfprintf function in stdio-common/vfprintf.c in glibc 2.14 and other versions allows context-dependent attackers to bypass the FORTIFY_SOURCE protection mechanism, conduct format string attacks, and write to arbitrary memory via a large number of arguments.
https://bugzilla.redhat.com/show_bug.cgi?id=794766
http://sourceware.org/git/?p=glibc.git%3Ba=commitdiff%3Bh=7c1f4834d398163d1ac8101e35e9c36fc3176e6e
http://rhn.redhat.com/errata/RHSA-2012-0531.html
http://rhn.redhat.com/errata/RHSA-2012-0488.html