Last updated 24 July 2024

Last updated 3 April 2025

Using the --fragment option in certain configuration setups OpenVPN version 2.6.0 to 2.6.6 allows an attacker to trigger a divide by zero behaviour which could cause an application crash, leading to a denial of service.

Last updated 24 July 2024

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

furlongm openvpn-monitor through 1.1.3 allows CSRF to disconnect an arbitrary client.

furlongm openvpn-monitor through 1.1.3 allows %0a command injection via the OpenVPN management interface socket. This can shut down the server via signal%20SIGTERM.

furlongm openvpn-monitor through 1.1.3 allows Authorization Bypass to disconnect arbitrary clients.

Control Channel in OpenVPN 2.4.7 and earlier allows remote attackers to cause a denial of service via crafted reset packet.

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.

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 the OpenVPN service pipe to be accessed remotely, which allows a remote attacker to interact with the privileged OpenVPN interactive service.

Unspecified vulnerability in OpenVPN 2.1-beta14 through 2.1-rc8, when running on non-Windows systems, allows remote servers to execute arbitrary commands via crafted (1) lladdr and (2) iproute configuration directives, probably related to shell metacharacters.

According to the upstream security report [1] the following flaw was found in OpenVPN 2.3.0 and earlier:

OpenVPN 2.3.0 and earlier running in UDP mode are subject to chosen ciphertext injection due to a non-constant-time HMAC comparison function. Plaintext recovery may be possible using a padding oracle attack on the CBC mode cipher implementation of the crypto library, optimistically at a rate of about one character per 3 hours. PolarSSL seems vulnerable to such an attack; the vulnerability of OpenSSL has not been verified or tested.

OpenVPN servers are typically configured to silently drop packets with the wrong HMAC. For this reason measuring the processing time of the packets is not trivial without a MITM position. In practice, the attack likely needs some target-specific information to be effective.

The severity of this vulnerability can be considered low. Only if OpenVPN is configured to use a null-cipher, arbitrary plain-text can be injected which can completely open up this attack vector.

A fix has been committed to git [2]; this is corrected in OpenVPN 2.3.1 and later.

[1] https://community.openvpn.net/openvpn/wiki/SecurityAnnouncement-f375aa67cc [2] https://github.com/OpenVPN/openvpn/commit/11d21349a4e7e38a025849479b36ace7c2eec2ee

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.

OpenVPN 2.5.1 and earlier versions allows a remote attackers to bypass authentication and access control channel data on servers configured with deferred authentication, which can be used to potentially trigger further information leaks.