The OpenVPN community has released a critical update after discovering a vulnerability that could lead to denial-of-service (DoS) attacks on servers configured with tls-crypt-v2.
OpenVPN, one of the most widely used systems globally for establishing virtual private networks (VPNs), has been affected by a security vulnerability that could allow attackers to cause unexpected shutdowns of VPN servers and disrupt encrypted communications. The developer community has responded by releasing version 2.6.14, which addresses this serious issue classified as CVE-2025-2704.
A flaw in packet authentication can crash servers
The vulnerability affects all versions between OpenVPN 2.6.1 and 2.6.13, but only when configured with the --tls-crypt-v2 option, a feature designed to encrypt and authenticate TLS control channels and enhance privacy against deep packet inspections (DPI).
The bug allows a specific combination of network packets —some valid and others malformed— to corrupt the client state on the server upon receipt. As a result, an internal protection mechanism triggers an ASSERT message and forces the immediate service interruption. If the VPN server is operating in a production environment, this crash can affect hundreds or thousands of users simultaneously.
Although the flaw does not allow access to encrypted data or the execution of malicious code, its disruptive potential is significant. The OpenVPN community clarifies that the flaw does not compromise the cryptographic integrity of the protocol.
Attack requirements and recommendations
To exploit this vulnerability, an attacker would need a valid client key for tls-crypt-v2 or the ability to intercept and inject manipulated packets during the TLS handshake phase.
Project maintainers recommend updating immediately to version OpenVPN 2.6.14. If updating is not feasible in the short term, it is advised to disable the --tls-crypt-v2 option, although this may result in a loss of privacy and resilience against certain types of monitoring.
What is OpenVPN and why is it so important?
OpenVPN is open-source software that enables the creation of secure tunnels over the Internet. Used by both businesses and individuals, it has built a solid reputation for its reliability, security, and flexibility. Unlike other proprietary solutions, OpenVPN allows for deep customization of the communication channel and is compatible with multiple operating systems, including Linux, Windows, macOS, Android, and iOS.
Additionally, its modular architecture has allowed for the addition of extra layers of security, such as tls-auth and tls-crypt, and more recently, tls-crypt-v2, which provides greater protection against traffic analysis and spoofing attacks.
This new incident demonstrates that even the most mature and robust solutions are not immune to critical flaws. The rapid response from the community showcases OpenVPN’s commitment to security but also serves as a reminder of the importance of keeping systems up to date and periodically reviewing critical configurations.
For more technical information about the vulnerability and update instructions, you can refer to the official notice published by the OpenVPN team:
👉 https://community.openvpn.net/openvpn/wiki/CVE-2025-2704