The l2tp_ip6_recvmsg function in net/l2tp/l2tp_ip6.c in the Linux kernel before 3.9-rc7 does not initialize a certain structure member, which allows local users to obtain sensitive information from kernel stack memory via a crafted recvmsg or recvfrom system call.
https://lkml.org/lkml/2013/4/14/107
https://github.com/torvalds/linux/commit/b860d3cc62877fad02863e2a08efff69a19382d2
http://www.ubuntu.com/usn/USN-1837-1
http://www.openwall.com/lists/oss-security/2013/04/14/3
http://lists.opensuse.org/opensuse-updates/2013-12/msg00129.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-May/104480.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-April/103750.html