Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-07-30T16:36:41 openvpn: OpenVPN: Denial of Service via crafted NTLM proxy response 5.3 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H CWE-787

OpenVPN version 2.1.0 through 2.6.20 and 2.7_alpha1 through 2.7.4 allows attackers via an off-by-one buffer write in the NTLM proxy authentication to potentially cause a crash via a crafted NTLM response from a malicious proxy server

A flaw was found in OpenVPN. A remote attacker could exploit an off-by-one buffer write vulnerability during NTLM (NT LAN Manager) proxy authentication. By sending a specially crafted NTLM response from a malicious proxy server, the attacker could cause the OpenVPN client to crash, leading to a denial of service.

This Moderate impact flaw in OpenVPN clients allows a denial of service via an off-by-one buffer write during NTLM proxy authentication. Exploitation requires a client to connect through a malicious NTLM proxy server, which can then send a specially crafted response. The necessity of user interaction with a compromised proxy limits the overall risk. https://www.cve.org/CVERecord?id=CVE-2026-11771 https://nvd.nist.gov/vuln/detail/CVE-2026-11771 https://community.openvpn.net/ReleaseHistory#openvpn-2621-released-1-july-2026 https://community.openvpn.net/ReleaseHistory#openvpn-275-released-1-july-2026 https://community.openvpn.net/Security%20Announcements/CVE-2026-11771