Executive brief
fetchmail is a mail delivery utility that retrieves email from remote servers. When compiled with NTLM support, a compromised or malicious mail server can send a specially crafted authentication challenge that causes fetchmail to overflow a stack buffer. This could allow an attacker to execute arbitrary code, or cause the application to crash.
Technical details
Stack-based buffer overflow in NTLM authentication handling when fetchmail is built with --enable-NTLM. A malicious mail server sends a crafted NTLM Type 2 challenge, causing fetchmail to write past a fixed stack buffer while constructing the authenticate response. Attack requires network connectivity to a mail server and occurs during NTLM authentication negotiation; exploitation may yield remote code execution depending on stack frame layout, though memory hardening may limit impact to authentication failure or process termination.
Affected products
- fetchmail 5.0.8 through 6.6.6
Timeline
- 2026-09-21: disclosed