CVE-2012-2751 in HTTP Server
Summary
by MITRE
ModSecurity before 2.6.6, when used with PHP, does not properly handle single quotes not at the beginning of a request parameter value in the Content-Disposition field of a request with a multipart/form-data Content-Type header, which allows remote attackers to bypass filtering rules and perform other attacks such as cross-site scripting (XSS) attacks. NOTE: this vulnerability exists because of an incomplete fix for CVE-2009-5031.
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Analysis
by VulDB Data Team • 06/18/2024
The vulnerability described in CVE-2012-2751 represents a critical flaw in the ModSecurity web application firewall implementation when processing HTTP requests containing multipart/form-data content with specific handling of single quotes in the Content-Disposition field. This issue affects ModSecurity versions prior to 2.6.6 and specifically manifests when PHP is used as the web server module, creating a dangerous condition that undermines the security controls designed to protect web applications from malicious input. The flaw stems from an incomplete remediation of a previously identified vulnerability CVE-2009-5031, indicating a pattern of security regressions that can leave applications exposed to sophisticated attack vectors.
The technical root cause of this vulnerability lies in ModSecurity's insufficient parsing logic for the Content-Disposition header within multipart requests. When a request contains a multipart/form-data Content-Type header and includes a Content-Disposition field with parameter values that contain single quotes not positioned at the beginning of the parameter value, ModSecurity fails to properly sanitize or recognize these input sequences. This parsing deficiency creates a bypass mechanism that allows malicious actors to inject crafted payloads that evade the normal filtering rules. The vulnerability specifically targets the way ModSecurity processes parameter values in HTTP headers, where single quotes are treated as delimiters or escape characters in certain contexts but are not consistently handled across all parameter positions.
The operational impact of this vulnerability extends beyond simple bypassing of security rules to enable more serious attack vectors including cross-site scripting attacks that can compromise user sessions and data integrity. Attackers can exploit this weakness to inject malicious scripts into web applications that would normally be blocked by ModSecurity's filtering mechanisms, potentially leading to unauthorized access, data exfiltration, or complete application compromise. The vulnerability particularly affects web applications that rely on ModSecurity for protection against common web attacks, creating a false sense of security while leaving critical input validation gaps open for exploitation. This issue demonstrates how seemingly minor parsing inconsistencies can create significant security weaknesses in web application firewalls that are meant to provide comprehensive protection.
Organizations using affected ModSecurity versions should immediately implement the available patch updates to version 2.6.6 or later, which contains the corrected parsing logic for Content-Disposition headers. Security teams should also conduct comprehensive audits of their existing ModSecurity configurations to identify any custom rules that may be similarly affected by parameter handling inconsistencies. Additional mitigations include implementing redundant security controls such as input validation at multiple layers, regular security testing of web application firewalls, and monitoring for anomalous request patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and represents a specific instance of the broader ATT&CK technique T1071.004 for application layer protocol tunneling that can be leveraged to bypass security controls. Organizations should also consider implementing additional security measures such as Content Security Policy headers, proper input sanitization, and regular security assessments to reduce the attack surface and improve overall resilience against similar vulnerabilities.