Microsoft ISA Server HTTP Request Smuggling Vulnerability



Date Discovered

June 14, 2005


Microsoft Internet Security and Acceleration (ISA) server is reported prone to a HTTP request smuggling attack. The vendor reports that Microsoft ISA server fails to correctly handle an invalid HTTP request that contains multiple 'Content-Length' values in an invalid HTTP header. A remote attacker may exploit this issue to launch cache poisoning or content-restriction bypass attacks against the affected 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


Deploy network intrusion detection systems to monitor network traffic for malicious activity.
Flag on anomalous HTTP requests that contain two 'Content-length' values. Audit logs regularly and adjust policies according to results.

Microsoft has released a fix to address this issue.



Steve Orrin of Watchfire is credited with the discovery of this issue.

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