CVE-2026-11771 - NTLM proxy auth stack off-by-one write

OpenVPN 2.x 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.

OpenVPN version 2.1.0 through 2.6.20 and 2.7_alpha1 through 2.7.4 are affected. This is fixed in versions 2.6.21 and 2.7.5.

CVE Record: CVE-2026-11771

Github:

• OpenVPN/openvpn-private-issues#116

Release notes:

• openvpn-2.7.5
• openvpn-2.6.21

Reported-By: Tristan Madani (@TristanInSec)