Buffer overflow in the POP3 server in 1st Class Mail Server 4.0 allows remote attackers to cause a denial of service (crash) and possibly execute arbitrary code via an APOP USER command with a long second parameter (digest).

Directory traversal vulnerability in 1st Class Mail Server 4.01 allows remote attackers to read arbitrary files via a ".." (dot dot) sequences in unknown vectors.

Cross-site scripting (XSS) vulnerability in 1st Class Mail Server 4.01 allows remote attackers to inject arbitrary web script or HTML via the Mailbox parameter to (1) viewmail.tagz, (2) the index script under /user/, (3) members.tagz, (4) general.tagz, (5) advanced.tagz, or (6) list.tagz.