CVE-2026-11771
Description
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.
Statement
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.
Understanding the Weakness (CWE)
Integrity
Technical Impact: Modify Memory; Execute Unauthorized Code or Commands
Write operations could cause memory corruption. In some cases, an adversary can modify control data such as return addresses in order to execute unexpected code.
Availability
Technical Impact: DoS: Crash, Exit, or Restart
Attempting to access out-of-range, invalid, or unauthorized memory could cause the product to crash.
Other
Technical Impact: Unexpected State
Subsequent write operations can produce undefined or unexpected results.
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