OpenVPN Flaw Allows Attackers Crash Servers and Run Remote Code
OpenVPN, a widely-used open-source virtual private network (VPN) software, has recently patched a security vulnerability that could allow attackers to crash servers and potentially execute remote code under certain conditions.
The flaw, identified as CVE-2025-2704, affects OpenVPN servers using specific configurations and has been addressed in the newly released version OpenVPN 2.6.14.
CVE-2025-2704: Overview
The vulnerability is specific to OpenVPN servers running versions 2.6.1 to 2.6.13 and using the –tls-crypt-v2 configuration.
It allows an attacker with a valid tls-crypt-v2 client key or network observation of a handshake using such a key to send a combination of authenticated and malformed packets.
These packets trigger an ASSERT() message, causing the server to abort unexpectedly.
While no cryptographic integrity is violated, no data is leaked, and remote code execution is not directly possible, the vulnerability poses a denial-of-service (DoS) risk for affected servers.
Fortunately, OpenVPN clients are unaffected by this bug.
The flaw was discovered by internal quality assurance testing at OpenVPN Inc., demonstrating the importance of rigorous internal security assessments.
Affected Products
A detailed table of affected products and versions is provided below:
| Product | Version | Vulnerability Impact |
| OpenVPN Server | 2.6.1 to 2.6.13 | Possible crash via malformed packets |
| OpenVPN Server (using tls-crypt-v2) | 2.6.1 to 2.6.13 | Risk of denial-of-service attack |
| OpenVPN Client | All versions | Not affected |
OpenVPN’s Response and Fixes
OpenVPN has released version 2.6.14 to address this security issue. This update includes the patch for CVE-2025-2704 and several other minor bug fixes:
- Security Fix: The patch ensures that malformed packets no longer lead to server crashes.
- Bug Fixes: Improvements include Linux DCO enhancements for source IP selection using –multihome and updates to the Windows MSI installer.
The updated version is built against OpenSSL 3.4.1, ensuring the latest security protocols.
How to Update
To mitigate the risks posed by CVE-2025-2704, administrators should upgrade their OpenVPN servers to the latest version (2.6.14).
The update is available for Windows, Linux, and FreeBSD systems, with installation files and GnuPG signatures provided on OpenVPN’s official website.
OpenVPN recommends that users regularly audit server configurations, especially when using advanced features like –tls-crypt-v2.
For servers running prior versions, disabling –tls-crypt-v2 temporarily may reduce exposure until the update is applied.
While the CVE-2025-2704 flaw highlights the potential vulnerabilities in complex VPN configurations, OpenVPN’s prompt response and active commitment to security underscore its reliability as a trusted VPN solution for businesses and individuals worldwide.
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