CVE-2003-1306 in URLScan
Summary
by MITRE
Microsoft URLScan 2.5, with the RemoveServerHeader option enabled, allows remote attackers to obtain sensitive information (server name and version) via an HTTP request that generates certain errors such as 400 "Bad Request," which leak the Server header in the response.
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Analysis
by VulDB Data Team • 07/04/2017
The vulnerability described in CVE-2003-1306 represents a significant information disclosure issue within Microsoft URLScan 2.5, a security tool designed to filter and sanitize HTTP requests to protect web servers from various attacks. This flaw specifically manifests when the RemoveServerHeader option is enabled, which should theoretically prevent the exposure of server identification information. However, the vulnerability demonstrates that certain error responses can still leak server metadata through the HTTP Server header, creating an unintended information disclosure channel that adversaries can exploit to gather intelligence about the target system.
The technical mechanism behind this vulnerability involves the interaction between URLScan's configuration and the HTTP response handling process. When the RemoveServerHeader setting is active, it typically strips the Server header from normal HTTP responses to prevent attackers from identifying the web server type and version. However, during specific error conditions such as HTTP 400 "Bad Request" responses, the URLScan module fails to properly sanitize the Server header, allowing it to leak through the error response. This occurs because the error handling code path bypasses the normal header removal process, creating a security gap that attackers can leverage to discover sensitive server information.
The operational impact of this vulnerability extends beyond simple information gathering, as it provides attackers with critical system intelligence that can be used for subsequent attacks. When an attacker discovers the server name and version through this information disclosure, they gain valuable knowledge about the underlying web server software, which can then be used to identify known vulnerabilities specific to that server version. This intelligence can significantly reduce the attack surface and increase the effectiveness of targeted exploitation attempts. The vulnerability essentially undermines the security posture of systems relying on URLScan for protection, as it creates a persistent information leak that persists even when other security measures are properly configured.
This vulnerability aligns with CWE-200, which addresses "Information Exposure," and demonstrates how seemingly defensive security configurations can create unintended attack vectors. The flaw also relates to ATT&CK technique T1082, "System Information Discovery," where adversaries gather information about the target system to inform their attack strategies. Organizations implementing URLScan 2.5 should consider this vulnerability as part of their broader security assessment, particularly when evaluating the effectiveness of their web server hardening measures. The issue highlights the importance of comprehensive testing of security tools under various error conditions and the need for thorough validation of security configurations to ensure they function correctly across all possible response scenarios. Mitigation strategies should include updating to newer versions of URLScan where this issue has been addressed, implementing additional network-level protections, and conducting regular security assessments to identify similar configuration gaps that could create information leakage channels.