A stack-based buffer overflow occurs in fetchmail when it is built with NTLM support. A malicious or compromised mail server that advertises NTLM authentication can issue a crafted Type 2 challenge, causing fetchmail to write beyond a fixed-size stack buffer while constructing the NTLM authentication response. Depending on the stack‑frame layout, this flaw can lead to remote code execution, or it may simply cause authentication failure or process termination under memory hardening. This vulnerability is classified as CWE‑121.

The flaw affects all Red Hat Enterprise Linux releases that ship or run fetchmail with the --enable‑NTLM build option. This includes RHEL 10, RHEL 9, RHEL 8, RHEL 7, and RHEL 6 when the offending binary is present.

The CVSS base score of 5.3 denotes medium severity, while the EPSS score of less than 1 % indicates a very low probability of widespread exploitation. The vulnerability is not listed in the CISA KEV catalog. The likely attack vector is remote over the network: an adversary who controls or compromises a mail server that advertises NTLM authentication can send a malicious NTLM challenge to a client running the vulnerable fetchmail. Successful exploitation typically requires that the client perform NTLM authentication and that the stack layout be favorable; modern stack hardening mitigates but does not eliminate the risk.