Microsoft Outlook Express NNTP Response Parsing Buffer Overflow Vulnerability



Date Discovered

June 14, 2005


Microsoft Outlook Express is prone to a buffer overflow when parsing NNTP responses. Successful exploits could allow arbitrary code to run in the context of the user running the application.

Technologies Affected

  • Microsoft Outlook Express 5.0
  • Microsoft Outlook Express 5.5
  • Microsoft Outlook Express 5.5 SP1
  • Microsoft Outlook Express 5.5 SP2
  • Microsoft Outlook Express 6.0
  • Microsoft Outlook Express 6.0 SP1


Block external access at the network boundary, unless external parties require service.
Block outgoing connections to NNTP services on TCP/UDP port 119 if such access is not explicitly required. If appropriate, allow outgoing connections to trusted servers only.

Do not use client software to access unknown or untrusted hosts from critical systems.
This vulnerability could be exploited only by connecting to a malicious NNTP server. Connect to only known or trusted NNTP servers from critical systems.

Implement multiple redundant layers of security.
Memory-protection schemes such as nonexecutable stack/heap configurations and randomly mapped memory segments may complicate exploitation of memory-corruption vulnerabilities.

Run all software as a nonprivileged user with minimal access rights.
Attackers could exploit this vulnerability to execute arbitrary code in the security context of the current user. Running applications as an unprivileged user with minimal access rights will limit the consequences of successful exploitation of this and other latent vulnerabilities.

Microsoft has released fixes for supported versions of the software.



Reported by an anonymous source.

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