A stack-based buffer overflow flaw was found in fetchmail when built with NTLM support. A malicious or compromised mail server advertising NTLM authentication can send a crafted Type 2 challenge that causes fetchmail to write past a fixed stack buffer while building the NTLM authenticate response. This may lead to remote code execution depending on stack-frame layout, or to authentication failure or process termination under memory hardening. Affects v5.0.8 through v6.6.6.
https://www.openwall.com/lists/oss-security/2026/06/27/8
https://www.fetchmail.info/fetchmail-SA-2026-01.txt
https://gitlab.com/fetchmail/fetchmail/-/commit/cb5be5c38471eec19e519ace0bc569176317ea92
https://bugzilla.redhat.com/show_bug.cgi?id=2537395