OpenVPN before 2.0.1 does not properly flush the OpenSSL error queue when a packet can not be decrypted by the server, which allows remote authenticated attackers to cause a denial of service (client disconnection) via a large number of packets that can not be decrypted.
http://www.securityfocus.com/bid/14607
http://www.mandriva.com/security/advisories?name=MDKSA-2005:145
http://www.debian.org/security/2005/dsa-851
http://secunia.com/advisories/17103