Date Discovered April 14, 2009
Description Microsoft ISA (Internet Security and Acceleration) Server and Forefront Threat Management Gateway (TMG) are prone to a cross-site scripting vulnerability because the software fails to properly sanitize user-supplied input.
An attacker may leverage this issue to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may help the attacker steal potentially sensitive information and launch other attacks.
- Microsoft Forefront Threat Management Gateway Medium Business Edition
- Microsoft ISA Server 2006
- Microsoft ISA Server 2006 SP1
- Microsoft ISA Server 2006 Supportability Update
Run all software as a nonprivileged user with minimal access rights. Attackers may successfully exploit client flaws in the browser through cross-site scripting vulnerabilities. When possible, run client software as regular user accounts with limited access to system resources. This may limit the immediate consequences of client-side vulnerabilities.
Deploy network intrusion detection systems to monitor network traffic for malicious activity. Deploy NIDS to detect and block attacks and anomalous activity such as requests containing suspicious URI sequences. Since the webserver may log such requests, review its logs regularly.
Do not follow links provided by unknown or untrusted sources. Web users should be cautious about following links to sites that are provided by unfamiliar or suspicious sources. Filtering HTML from emails may help remove a possible vector for transmitting malicious links to users.
Set web browser security to disable the execution of script code or active content.
Since a successful exploit of this issue allows malicious code to execute in web clients, consider disabling support for script code and active content within the client browser. Note that this mitigation tactic might adversely affect legitimate websites that rely on the execution of browser-based script code.
The vendor has released an advisory and updates. Please see the referenced advisory for details.
Credits Michael Jordan of Context Information Security
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