The l2tp_ip_recvmsg function in net/l2tp/l2tp_ip.c in the Linux kernel before 3.12.4 updates a certain length value before ensuring that an associated data structure has been initialized, which allows local users to obtain sensitive information from kernel stack memory via a (1) recvfrom, (2) recvmmsg, or (3) recvmsg system call.
https://github.com/torvalds/linux/commit/bceaa90240b6019ed73b49965eac7d167610be69
https://bugzilla.redhat.com/show_bug.cgi?id=1035875
http://www.ubuntu.com/usn/USN-2141-1
http://www.ubuntu.com/usn/USN-2139-1
http://www.ubuntu.com/usn/USN-2138-1
http://www.ubuntu.com/usn/USN-2136-1
http://www.ubuntu.com/usn/USN-2135-1
http://www.ubuntu.com/usn/USN-2117-1
http://www.ubuntu.com/usn/USN-2113-1
http://www.ubuntu.com/usn/USN-2110-1
http://www.ubuntu.com/usn/USN-2109-1
http://www.ubuntu.com/usn/USN-2108-1
http://www.ubuntu.com/usn/USN-2107-1
http://www.openwall.com/lists/oss-security/2013/11/28/13
http://www.kernel.org/pub/linux/kernel/v3.x/ChangeLog-3.12.4
http://secunia.com/advisories/56036
http://secunia.com/advisories/55882
http://seclists.org/oss-sec/2014/q1/29
http://lists.opensuse.org/opensuse-security-announce/2014-03/msg00026.html