CVE-2025-2704: 
OpenVPN vulnerability analysis and mitigation

OpenVPN versions 2.6.1 through 2.6.13 contain a critical security vulnerability (CVE-2025-2704) that affects servers running in TLS-crypt-v2 mode. The vulnerability was discovered through internal quality assurance testing at OpenVPN Inc and was disclosed on April 2, 2025. The issue has been fixed in OpenVPN version 2.6.14 (OpenWall, SecurityOnline).

The vulnerability allows remote attackers to trigger a denial of service condition by sending a specific combination of authenticated and malformed packets during the early handshake phase. To exploit the vulnerability, an attacker must either possess a valid tls-crypt-v2 client key or be able to monitor network traffic during a TLS handshake with a valid client key. When triggered, the server experiences client state corruption that leads to an ASSERT() message and immediate termination. The vulnerability has been assigned a CVSS v3.1 base score of 7.5 (HIGH) with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (NVD, SecurityOnline).

When successfully exploited, the vulnerability results in an immediate server crash, causing a denial of service condition that can disrupt VPN services for all connected users. However, the vulnerability does not compromise cryptographic integrity, leak sensitive data, or enable remote code execution. The impact is limited to OpenVPN servers, as clients are not affected by this vulnerability (OpenWall, SecurityOnline).

The primary mitigation is to upgrade to OpenVPN version 2.6.14, which contains the security fix for this vulnerability. For systems where immediate upgrade is not possible, administrators can temporarily disable the --tls-crypt-v2 option as a workaround, though this may reduce privacy features (SecurityOnline).