CVE-2026-94184 describes a stack-based buffer overflow in fetchmail's NTLM authentication implementation. When fetchmail is built with NTLM support, a malicious or compromised mail server can send a specially crafted NTLM Type 2 challenge that causes fetchmail to overflow a fixed stack buffer during the construction of the NTLM authenticate response. This vulnerability can result in remote code execution depending on the stack frame layout or cause authentication failures or process termination under memory hardening conditions. The vulnerability affects fetchmail versions 5.0.8 through 6.6.6. Red Hat advisory confirms the issue and recommends either rebuilding fetchmail without NTLM support or upgrading to version 6.6.7 or later.

The vulnerability allows a remote attacker controlling a mail server to potentially execute arbitrary code on the client running fetchmail if NTLM support is enabled. Alternatively, it may cause authentication failures or process crashes, impacting availability. The CVSS v3.1 score is 8.1, indicating high severity with network attack vector, high impact on confidentiality, integrity, and availability, and no privileges or user interaction required.

Red Hat advises rebuilding fetchmail without NTLM support by omitting the --enable-NTLM option at configure time or upgrading to fetchmail version 6.6.7 or later. Confirm the absence of NTLM support by running 'fetchmail -V' and verifying that '+NTLM' is not listed. These are the recommended and effective mitigations.