OpenVPN version 2.4.0 through 2.6.10 on Windows allows an external, lesser privileged process to create a named pipe which the OpenVPN GUI component would connect to allowing it to escalate its privileges
OpenVPN version 2.6.1 through 2.6.13 in server mode using TLS-crypt-v2 allows remote attackers to trigger a denial of service by corrupting and replaying network packets in the early handshake phase
OpenVPN before 2.6.11 does not santize PUSH_REPLY messages properly which an attacker controlling the server can use to inject unexpected arbitrary data ending up in client logs.
OpenVPN from 2.6.0 through 2.6.10 in a server role accepts multiple exit notifications from authenticated clients which will extend the validity of a closing session