Mercury Mail Transport System AUTH CRAM-MD5 Buffer Overflow Vulnerability



Date Discovered

August 18, 2007


Mercury Mail Transport System is prone to a remote stack-based buffer-overflow vulnerability because it fails to perform adequate boundary checks when handling AUTH CRAM-MD5 requests. Attackers can exploit this issue to execute arbitrary code with the privileges of the user running the application. Successful exploits will compromise the computer. Failed exploit attempts will result in a denial of service. Versions prior to Mercury/32 v4.52 and Mercury/NLM v1.49 are vulnerable. UPDATE (August 28, 2007): Symantec has confirmed that this issue is being actively exploited in the wild.

Technologies Affected

  • Pegasus Mail Mercury Mail Transport System 4.01B
  • Pegasus Mail Mercury Mail Transport System 4.51


Block external access at the network boundary, unless external parties require service.
If global access isn't needed, filter access to the affected computer at the network boundary. Restricting access to only trusted computers and networks might greatly reduce the likelihood of successful exploits.

Run all software as a nonprivileged user with minimal access rights.
To reduce the impact of latent vulnerabilities, always run nonadministrative software as an unprivileged user with minimal access rights.

Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy NIDS to monitor network traffic for signs of anomalous or suspicious activity. This includes but is not limited to requests that include NOP sleds and unexplained incoming and outgoing traffic. This may indicate exploit attempts or activity that results from successful exploits.

Implement multiple redundant layers of security.
Since this issue may be leveraged to execute code, we recommend memory-protection schemes, such as nonexecutable stack/heap configurations and randomly mapped memory segments. This tactic may complicate exploits of memory-corruption vulnerabilities.

The vendor released updates to address this issue. Please see the references for more information.



eliteb0y is credited with the discovery of this issue.

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