Title: Authentication Error in SMTP Service Could Allow Mail
Relaying
Date: 05 July, 2001
Software: Windows 2000
Impact: Mail Relaying
Bulletin: MS01-037

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-037.asp.

Issue:

An SMTP service installs by default as part of Windows 2000 server
products, and can be selected for installation on Windows 2000
Professional. A vulnerability results because of a flaw in the
authentication process used by the service. The vulnerability could
allow an unauthorized user to successfully authenticate to the
service using incorrect credentials. An attacker who exploited
the vulnerability could gain user-level privileges on the SMTP
service, thereby enabling the attacker to use the service but
not to administer it. The most likely purpose in exploiting the
vulnerability would be to perform mail relaying via the server.

Mitigating Factors:

• Exchange servers – even when run on Windows 2000 –
  are not affected by this vulnerability.
• Best practices recommend disabling unneeded services.
  If the SMTP service has been disabled, the
  vulnerability could not be exploited.
• The vulnerability only affects stand-alone machines,
  not domain members.
• Proper firewalling could prevent Internet-based attacks
  by blocking port 25 on servers that do not specifically
  need to accept SMTP traffic.

Patch Availability:

• A patch is available to fix this vulnerability. Please read
  the Security Bulletin
  http://www.microsoft.com/technet/security/bulletin/ms01-037.asp
  for information on obtaining this patch.

Acknowledgment:

• Joao Gouveia ([email protected])

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