CVE-2005-2089 in IIS
Summary
by MITRE
Microsoft IIS 5.0 and 6.0 allows remote attackers to poison the web cache, bypass web application firewall protection, and conduct XSS attacks via an HTTP request with both a "Transfer-Encoding: chunked" header and a Content-Length header, which causes IIS to incorrectly handle and forward the body of the request in a way that causes the receiving server to process it as a separate HTTP request, aka "HTTP Request Smuggling."
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Analysis
by VulDB Data Team • 04/13/2019
Microsoft IIS 5.0 and 6.0 contain a critical vulnerability classified as HTTP request smuggling that arises from improper handling of conflicting HTTP headers. This flaw occurs when an attacker submits an HTTP request containing both a Transfer-Encoding: chunked header and a Content-Length header simultaneously. The vulnerability stems from the server's inability to properly interpret these contradictory headers, creating a condition where the web server processes the request body in an unexpected manner. The underlying technical issue manifests as a failure in HTTP protocol parsing, where IIS cannot correctly determine whether to process the request body as a chunked transfer or as a length-based payload.
The operational impact of this vulnerability extends beyond simple cache poisoning to encompass sophisticated attack vectors that can bypass security controls and execute cross-site scripting payloads. When IIS encounters the conflicting headers, it incorrectly forwards the request body in a manner that allows subsequent processing by the receiving server to interpret the body as a separate HTTP request. This creates a scenario where an attacker can smuggle malicious requests through the web server, effectively bypassing web application firewall protections that rely on proper HTTP parsing. The vulnerability enables attackers to manipulate how the server processes HTTP requests, potentially allowing them to access restricted resources or execute malicious code through XSS attacks that exploit the improper request handling.
This vulnerability directly maps to CWE-444, which describes improper handling of HTTP requests, and aligns with ATT&CK technique T1190 for exploiting vulnerabilities in web applications. The flaw represents a fundamental issue in HTTP protocol implementation where servers fail to properly validate header combinations that are mutually exclusive. Security researchers have identified that this vulnerability can be leveraged to bypass various security controls including web application firewalls, intrusion detection systems, and content filtering mechanisms. The attack vector requires minimal privileges and can be executed remotely, making it particularly dangerous for web servers that process untrusted input from external sources.
Organizations affected by this vulnerability should implement immediate mitigations including disabling or restricting the use of Transfer-Encoding: chunked headers where possible, configuring web application firewalls to detect and block suspicious header combinations, and applying Microsoft security patches that address the HTTP parsing issues. Network segmentation and monitoring of HTTP traffic can help detect anomalous header patterns that may indicate exploitation attempts. Additionally, implementing proper input validation and sanitization at multiple layers of the application stack provides defense-in-depth against similar vulnerabilities. Regular security assessments and penetration testing should be conducted to identify other potential HTTP smuggling vectors that may exist in the organization's infrastructure.
The broader implications of this vulnerability highlight the critical importance of proper HTTP protocol implementation in web servers and the potential for seemingly minor parsing issues to create significant security risks. This flaw demonstrates how HTTP specification compliance issues can be exploited to bypass sophisticated security controls, emphasizing the need for comprehensive testing of HTTP request handling mechanisms. Organizations should review their web server configurations and ensure that they properly validate HTTP headers to prevent similar issues that could arise from other protocol ambiguities or implementation flaws. The vulnerability also underscores the importance of maintaining up-to-date security patches and implementing robust security monitoring to detect and respond to exploitation attempts.