CVE-2008-3906 in Mono
Summary
by MITRE
CRLF injection vulnerability in Sys.Web in Mono 2.0 and earlier allows remote attackers to inject arbitrary HTTP headers and conduct HTTP response splitting attacks via CRLF sequences in the query string.
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Analysis
by VulDB Data Team • 01/01/2025
The CVE-2008-3906 vulnerability represents a critical CRLF injection flaw within the Sys.Web framework component of Mono versions 2.0 and earlier. This vulnerability exists at the core of web application processing where the framework fails to properly sanitize user input containing carriage return line feed sequences. The flaw specifically manifests when processing query string parameters, allowing malicious actors to inject arbitrary HTTP headers into the response stream. The vulnerability operates by exploiting insufficient input validation mechanisms that should normally filter out or escape CRLF characters before they are processed as part of HTTP response construction. This particular weakness falls under the CWE-113 category of "Improper Neutralization of CRLF Sequences in HTTP Headers" and represents a classic example of how inadequate input sanitization can lead to severe security implications.
The technical exploitation of this vulnerability enables attackers to perform HTTP response splitting attacks, a sophisticated technique that can be leveraged for various malicious purposes including session hijacking, cross-site scripting, and cache poisoning. When an attacker crafts a query string containing CRLF sequences, these characters can be interpreted by the vulnerable Mono framework as delimiters between HTTP headers rather than as part of the intended parameter value. This allows the attacker to inject additional HTTP headers into the response, potentially including Set-Cookie headers, Content-Type modifications, or other headers that can alter the behavior of the web application. The vulnerability is particularly dangerous because it operates at the HTTP protocol level and can affect the entire response processing pipeline, making it a prime target for attackers seeking to manipulate web application behavior.
The operational impact of CVE-2008-3906 extends beyond simple header injection, as it can enable sophisticated attack vectors that compromise the integrity and confidentiality of web applications running on affected Mono platforms. Response splitting attacks enabled by this vulnerability can lead to session management bypasses where attackers can manipulate user sessions by injecting malicious headers that redirect or modify session cookies. Additionally, the vulnerability can facilitate cache poisoning attacks where maliciously crafted responses can be cached by intermediate proxies or browsers, potentially affecting multiple users. The vulnerability affects web applications that rely on Mono's Sys.Web framework for client-side script generation, particularly those that process user input through query parameters without proper sanitization. This creates a significant risk for enterprise applications that depend on Mono for web service implementation and could result in unauthorized access to sensitive data or system compromise.
Organizations affected by this vulnerability should implement immediate mitigations including upgrading to Mono versions 2.2 or later where the vulnerability has been addressed through improved input validation and sanitization mechanisms. The recommended approach involves comprehensive input validation that properly escapes or removes CRLF sequences from query string parameters before they are processed by the Sys.Web framework. Security teams should also implement web application firewalls that can detect and block suspicious CRLF sequences in HTTP requests, and conduct thorough code reviews to ensure that all user input is properly sanitized before being used in HTTP response construction. The vulnerability highlights the importance of following secure coding practices as outlined in the OWASP Top Ten and aligns with ATT&CK technique T1190 for "Exploit Public-Facing Application" and T1071.1001 for "Application Layer Protocol: Web Protocols" which emphasizes the need for proper input validation in web applications to prevent protocol-level attacks. Organizations should also consider implementing automated security scanning tools that can detect similar vulnerabilities in their codebase and establish regular security assessment procedures to identify and remediate such flaws before they can be exploited by threat actors.