CVE-2009-4086 in Xerver HTTP Server
Summary
by MITRE
CRLF injection vulnerability in Xerver HTTP Server 4.31 and 4.32 allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via certain byte sequences at the end of a URL. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 01/26/2025
The CVE-2009-4086 vulnerability represents a critical CRLF injection flaw in Xerver HTTP Server versions 4.31 and 4.32 that enables remote attackers to manipulate HTTP responses through carefully crafted byte sequences appended to URLs. This vulnerability falls under the CWE-113 category for improper neutralization of CRLF characters within HTTP headers, making it a prime example of HTTP response splitting vulnerability. The flaw exploits the server's insufficient input validation mechanisms when processing URLs that contain carriage return line feed sequences, allowing malicious actors to inject arbitrary HTTP headers into the response stream.
The technical implementation of this vulnerability occurs when the Xerver HTTP Server fails to properly sanitize URL parameters before processing them in the HTTP response generation phase. When a URL containing CRLF sequences is processed, the server does not adequately filter or escape these characters, permitting attackers to inject additional HTTP headers that can be interpreted by the client or intermediate proxies. This injection capability enables attackers to manipulate the HTTP response in ways that can bypass security controls, manipulate cached content, or redirect users to malicious destinations. The vulnerability specifically targets the server's handling of byte sequences at the end of URLs, making it particularly dangerous as it requires minimal payload complexity to exploit effectively.
The operational impact of CVE-2009-4086 extends beyond simple header injection to enable sophisticated attack vectors including session hijacking, cross-site scripting exploitation, and cache poisoning attacks. When successfully exploited, this vulnerability allows attackers to split HTTP responses, potentially causing web browsers to process malicious content as legitimate responses. The vulnerability is particularly concerning because it operates at the HTTP protocol level, affecting the fundamental trust model between web servers and clients. Attackers can leverage this weakness to create forged responses that appear legitimate to browsers and proxies, undermining security mechanisms such as content security policies and authentication controls. The impact is amplified by the fact that this vulnerability affects a widely used HTTP server implementation, making numerous systems potentially vulnerable to exploitation.
Mitigation strategies for CVE-2009-4086 should focus on implementing robust input validation and sanitization mechanisms at all points where user-supplied data enters the HTTP processing pipeline. Organizations should deploy web application firewalls that can detect and block CRLF injection attempts, while also ensuring that all HTTP servers are updated to versions that properly handle and escape CRLF characters in URL parameters. The implementation of proper header validation and the enforcement of strict HTTP response formatting rules can prevent attackers from injecting malicious headers. Additionally, network segmentation and monitoring solutions should be deployed to detect unusual HTTP traffic patterns that may indicate exploitation attempts. This vulnerability demonstrates the critical importance of input validation in web applications and aligns with ATT&CK technique T1190 for exploiting vulnerabilities in web applications, specifically targeting the manipulation of HTTP responses through injection attacks.