OpenVPN 2.x before 2.0.11, 2.1.x, 2.2.x before 2.2.3, and 2.3.x before 2.3.6 allows remote authenticated users to cause a denial of service (server crash) via a small control channel packet.
https://community.openvpn.net/openvpn/wiki/SecurityAnnouncement-97597e732b
http://www.ubuntu.com/usn/USN-2430-1
http://www.debian.org/security/2014/dsa-3084
http://lists.opensuse.org/opensuse-security-announce/2014-12/msg00008.html