CVE-2005-2088 in HTTP Server
Summary
by MITRE
The Apache HTTP server before 1.3.34, and 2.0.x before 2.0.55, when acting as an HTTP proxy, 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 Apache 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 • 07/05/2019
The vulnerability described in CVE-2005-2088 represents a critical HTTP request smuggling flaw that affected Apache HTTP server versions prior to 1.3.34 and 2.0.55 when operating in proxy mode. This vulnerability stems from the server's improper handling of conflicting HTTP headers that specify both Transfer-Encoding: chunked and Content-Length in the same request. The flaw occurs because different HTTP implementations interpret these conflicting headers differently, creating a parsing ambiguity that malicious actors can exploit to manipulate request processing. The vulnerability specifically targets the proxy functionality of Apache servers, where the server acts as an intermediary between client and origin server, making it a particularly dangerous issue for organizations that rely on Apache as a reverse proxy or forward proxy solution.
The technical exploitation of this vulnerability relies on the fundamental inconsistency in how HTTP parsers handle conflicting headers. When a client sends a request containing both Transfer-Encoding: chunked and Content-Length headers, the server must decide which header to honor for processing the request body. In vulnerable Apache versions, this decision process was flawed, causing the server to forward portions of the request body as if they were separate HTTP requests. This creates a situation where an attacker can inject malicious content that gets interpreted by the backend server as a completely separate request, potentially bypassing security mechanisms that were designed to protect against such attacks. The vulnerability is classified under CWE-444 as an improper handling of HTTP headers, specifically related to HTTP request smuggling techniques that exploit inconsistencies in protocol implementations.
The operational impact of this vulnerability extends beyond simple cache poisoning to encompass significant security implications including bypassing web application firewalls and enabling cross-site scripting attacks. When an attacker successfully exploits this vulnerability, they can manipulate the proxy server to forward malicious content that appears as legitimate requests to backend servers, effectively allowing them to circumvent security controls designed to detect and block malicious traffic. The cache poisoning aspect means that legitimate users might receive cached malicious content, while the bypass of web application firewalls creates a pathway for attackers to reach backend applications that would normally be protected. This vulnerability particularly affects organizations using Apache as a proxy server for web applications, making it a critical concern for enterprises that rely on Apache for load balancing, content caching, or security filtering functions.
Organizations affected by this vulnerability should implement immediate mitigations including upgrading to patched versions of Apache HTTP server, specifically versions 1.3.34 and 2.0.55 or later. Additional protective measures include configuring proxy servers to reject requests containing conflicting headers, implementing proper header validation at the network level, and monitoring for unusual patterns in HTTP request processing that might indicate exploitation attempts. Network administrators should also consider implementing intrusion detection systems that can identify suspicious header combinations and establish logging mechanisms to track proxy request handling behavior. The vulnerability demonstrates the importance of proper HTTP protocol implementation and the need for consistent interpretation of HTTP headers across different server implementations, aligning with ATT&CK technique T1571 for "Modify HTTP Headers" and emphasizing the critical nature of maintaining secure proxy configurations in enterprise environments.