OpenVPN 2.1.0-2.6.20 / 2.7_alpha1-2.7.4 Off-by-One in NTLM Proxy Auth
CVE-2026-11771 Published on July 30, 2026
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
Vulnerability Analysis
CVE-2026-11771 can be exploited with network access. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Types
What is an off-by-five Vulnerability?
A product calculates or uses an incorrect maximum or minimum value that is 1 more, or 1 less, than the correct value.
CVE-2026-11771 has been classified to as an off-by-five vulnerability or weakness.
What is a Stack Overflow Vulnerability?
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).
CVE-2026-11771 has been classified to as a Stack Overflow vulnerability or weakness.
What is a Memory Corruption Vulnerability?
The software writes data past the end, or before the beginning, of the intended buffer. Typically, this can result in corruption of data, a crash, or code execution. The software may modify an index or perform pointer arithmetic that references a memory location that is outside of the boundaries of the buffer. A subsequent write operation then produces undefined or unexpected results.
CVE-2026-11771 has been classified to as a Memory Corruption vulnerability or weakness.
Products Associated with CVE-2026-11771
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Affected Versions
OpenVPN:- Version 2.1.0, <= 2.6.20 is affected.
- Version 2.7_alpha1, <= 2.7.4 is affected.