Microsoft Exchange Server 5.5 and 5.0 does not properly handle (1) malformed NNTP data, or (2) malformed SMTP data, which allows remote attackers to cause a denial of service (application error).
Microsoft Exchange 5.5 allows a remote attacker to relay email (i.e. spam) using encapsulated SMTP addresses, even if the anti-relaying features are enabled.
The installation of 1ArcServe Backup and Inoculan AV client modules for Exchange create a log file, exchverify.log, which contains usernames and passwords in plaintext.