OpenVPN, when using a 64-bit block cipher, makes it easier for remote attackers to obtain cleartext data via a birthday attack against a long-duration encrypted session, as demonstrated by an HTTP-over-OpenVPN session using Blowfish in CBC mode, aka a "Sweet32" attack.

OpenVPN ovpn-dco for Windows version 1.1.1 allows an unprivileged local attacker to send I/O control messages with invalid data to the driver resulting in a NULL pointer dereference leading to a system halt.

OpenVPN Connect before version 3.5.0 can contain the configuration profile's clear-text private key which is logged in the application log, which an unauthorized actor can use to decrypt the VPN traffic

OpenVPN before 2.6.11 does not santize PUSH_REPLY messages properly which attackers can use to inject unexpected arbitrary data into third-party executables or plug-ins.

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

tap-windows6 driver version 9.26 and earlier does not properly check the size data of incomming write operations which an attacker can use to overflow memory buffers, resulting in a bug check and potentially arbitrary code execution in kernel space

OpenVPN plug-ins on Windows with OpenVPN 2.6.9 and earlier could be loaded from any directory, which allows an attacker to load an arbitrary plug-in which can be used to interact with the privileged OpenVPN interactive service.

The interactive service in OpenVPN 2.6.9 and earlier allows an attacker to send data causing a stack overflow which can be used to execute arbitrary code with more privileges.

The interactive service in OpenVPN 2.6.9 and earlier allows the OpenVPN service pipe to be accessed remotely, which allows a remote attacker to interact with the privileged OpenVPN interactive service.

The PKCS#7 parser in OpenVPN 3 Core Library versions through 3.8.3 did not properly validate the parsed data, which would result in the application crashing.