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
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.