SmarterTools SmarterMail versions prior to build 9518 contain an unauthenticated path coercion vulnerability in the background-of-the-day preview endpoint. The application base64-decodes attacker-supplied input and uses it as a filesystem path without validation. On Windows systems, this allows UNC paths to be resolved, causing the SmarterMail service to initiate outbound SMB authentication attempts to attacker-controlled hosts.

This can be abused for credential coercion, NTLM relay attacks, and unauthorized network authentication.