Microsoft Exchange Server SMTP Extended Verb Buffer Overflow Vulnerability



Date Discovered

April 12, 2005


Microsoft Exchange Server is prone to a buffer overflow in the X-LINK2STATE SMTP extended verb. Successful exploitation could result in arbitrary code execution.

Technologies Affected

  • Microsoft Exchange Server 2000
  • Microsoft Exchange Server 2000 SP1
  • Microsoft Exchange Server 2000 SP2
  • Microsoft Exchange Server 2000 SP3
  • Microsoft Exchange Server 2003 SP1
  • Microsoft Exchange Server 2003


Block external access at the network boundary, unless external parties require service.
Block access to the vulnerable service at the network perimeter. Restrict external access to trusted computers and networks.

Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy a network intrusion detection sensor between the affected service and the network perimeter. Audit the logs regularly for indications of potential attacks.

Run all software as a nonprivileged user with minimal access rights.
If possible, run the SMTP service as an unprivileged user with minimal access rights. This will limit the consequences of successful exploitation of this and other latent vulnerabilities.

Implement multiple redundant layers of security.
If possible, place the vulnerable server inside the network firewall and use an SMTP gateway to relay mail to the vulnerable server. Allow the vulnerable server to accept connections only from the SMTP gateway.

Microsoft has released updates to address this issue in supported versions.



Discovery is credited to Mark Dowd and Ben Layer.

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