CVE-2009-1902 in ModSecurity
Summary
by MITRE
The multipart processor in ModSecurity before 2.5.9 allows remote attackers to cause a denial of service (crash) via a multipart form datapost request with a missing part header name, which triggers a NULL pointer dereference.
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Analysis
by VulDB Data Team • 11/25/2024
The vulnerability identified as CVE-2009-1902 resides within the multipart processor component of ModSecurity, a widely deployed web application firewall solution that protects web applications from various attack vectors. This flaw specifically affects ModSecurity versions prior to 2.5.9 and represents a critical denial of service vulnerability that can be exploited by remote attackers to crash the web application firewall service. The vulnerability stems from inadequate input validation within the multipart form data processing logic, where the system fails to properly handle malformed multipart requests that lack essential header information.
The technical implementation of this vulnerability involves a NULL pointer dereference condition that occurs when ModSecurity attempts to process a multipart form data post request containing a part without a header name. In standard multipart form data encoding, each part should contain a Content-Disposition header that includes a name attribute identifying the form field. When this header name is missing or malformed, the multipart processor in affected ModSecurity versions does not properly validate the input structure before attempting to access the header information, leading to a situation where a null pointer is dereferenced during the parsing process. This fundamental error in memory management causes the application to crash and terminate unexpectedly, resulting in a denial of service condition that disrupts legitimate web application functionality.
The operational impact of CVE-2009-1902 extends beyond simple service disruption as it can be leveraged by attackers to create persistent availability issues for web applications protected by ModSecurity. The vulnerability is particularly concerning because it requires minimal effort to exploit and can be executed remotely without authentication, making it an attractive target for malicious actors seeking to disrupt web services. When exploited successfully, the crash affects the entire ModSecurity module, potentially leaving web applications without critical protection mechanisms during the service restart period. The vulnerability also represents a weakness in the input validation and error handling capabilities of the web application firewall, indicating broader architectural issues in how malformed requests are processed and managed within the security solution.
This vulnerability aligns with CWE-476, which specifically addresses NULL pointer dereference conditions in software implementations, and demonstrates the importance of robust input validation and error handling in security-critical applications. From an attack framework perspective, the vulnerability fits within the denial of service category of the MITRE ATT&CK framework, specifically relating to service availability compromise techniques that target infrastructure components. Organizations implementing ModSecurity should prioritize immediate patching to address this vulnerability, as the lack of proper input validation creates an attack surface that can be exploited to disrupt business operations and potentially mask more sophisticated attacks. The vulnerability also underscores the importance of comprehensive testing procedures for security tools, particularly in handling malformed inputs that may occur during legitimate user interactions or malicious exploitation attempts.