Microsoft ISA Server NetBIOS Predefined Filter Policy Bypass Vulnerability



Date Discovered

June 14, 2005


Microsoft Internet Security and Acceleration (ISA) server is prone to a policy bypass vulnerability. Reports indicate that the issue manifests when a Microsoft ISA server is utilizing the 'NetBIOS (all)' predefined filter. A remote attacker may leverage this vulnerability to successfully make NetBIOS connections to NetBIOS based services that exist on a target ISA server.

Technologies Affected

  • Microsoft ISA Server 2000
  • Microsoft ISA Server 2000 Enterprise Edition SP1
  • Microsoft ISA Server 2000 Enterprise Edition SP2
  • Microsoft ISA Server 2000 Enterprise Edition
  • Microsoft ISA Server 2000 FP1
  • Microsoft ISA Server 2000 SP1
  • Microsoft ISA Server 2000 SP2


Block external access at the network boundary, unless external parties require service.
Network access controls should be deployed to limit remote access to NetBIOS services on the affected computer. This may reduce the risk associated with this vulnerability.

Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Deploy an intrusion detect sensor. Flag on anomalous NetBIOS traffic, audit logs regularly for indications of potentially malicious attacks and adjust policies accordingly.

Microsoft has released a fix to address this issue.



The vendor reported this issue.

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