The openvpn_decrypt function in crypto.c in OpenVPN 2.3.0 and earlier, when running in UDP mode, allows remote attackers to obtain sensitive information via a timing attack involving an HMAC comparison function that does not run in constant time and a padding oracle attack on the CBC mode cipher.
http://lists.fedoraproject.org/pipermail/package-announce/2013-May/105568.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-May/105609.html
http://lists.opensuse.org/opensuse-updates/2013-11/msg00012.html
http://lists.opensuse.org/opensuse-updates/2013-11/msg00016.html
https://bugs.gentoo.org/show_bug.cgi?id=468756
https://bugzilla.redhat.com/show_bug.cgi?id=960192
https://github.com/OpenVPN/openvpn/commit/11d21349a4e7e38a025849479b36ace7c2eec2ee
http://www.mandriva.com/security/advisories?name=MDVSA-2013:167