Off-by-One Buffer Write Vulnerability in OpenVPN Affects Multiple Versions
CVE-2026-11771

7HIGH

Key Information:

Vendor

Openvpn
Status
Openvpn
Vendor
CVE Published:
30 July 2026

What is CVE-2026-11771?

OpenVPN versions ranging from 2.1.0 to 2.6.20 and 2.7_alpha1 to 2.7.4 contain a vulnerability that allows attackers to exploit the NTLM proxy authentication mechanism. An off-by-one buffer write could enable a malicious proxy server to craft a specific NTLM response, potentially leading to application crashes. This vulnerability highlights the importance of timely updates and vigilant monitoring of authentication protocols in OpenVPN.

Affected Version(s)

OpenVPN 2.1.0 <= 2.6.20

OpenVPN 2.7_alpha1 <= 2.7.4

References

https://community.openvpn.net/Security%20Announcements/CV...
vendor-advisory
https://community.openvpn.net/ReleaseHistory#openvpn-275-...
release-notes
https://community.openvpn.net/ReleaseHistory#openvpn-2621...
release-notes

CVSS V4

Score:
7
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
High
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
Unknown

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.