Microsoft Exchange fails to handle certain SMTP extended verbs correctly. In Exchange 5.5, this can lead to a denial-of-service condition. In Exchange 2000, this could permit an attacker to run arbitrary code.
Microsoft Exchange is a popular collaboration product which includes extensive support for electronic mail, including support for SMTP. SMTP is a standard protocol for exchanging electronic mail over the internet. Exchange uses SMTP to communicate special handling instructions from one Exchange server to another through the use of SMTP extended verbs. Exchange fails to process some of these commands correctly. On Exchange 5.5, the failure can result in a denial of service condition, and on Exchange 2000, it could result in an attacker running arbitrary code. For more information, see Microsoft Security Bulletin MS03-046.
An attacked could cause a denial of service condition against Exchange 5.5 or execute arbitrary code against Exchange 2000.
Apply a patch as described in Microsoft Security Bulletin MS03-046.
Thanks to Microsoft for reporting this vulnerability. Microsoft has credited João Gouveia for reporting this vulnerability.