CVE-2012-4528 in ModSecurity
Summary
by MITRE
The mod_security2 module before 2.7.0 for the Apache HTTP Server allows remote attackers to bypass rules, and deliver arbitrary POST data to a PHP application, via a multipart request in which an invalid part precedes the crafted data.
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Analysis
by VulDB Data Team • 10/25/2024
The vulnerability identified as CVE-2012-4528 represents a critical flaw in the mod_security2 module version 2.6.9 and earlier, which operates as a web application firewall for the Apache HTTP Server. This security issue stems from improper handling of multipart HTTP requests, specifically when invalid parts precede crafted data within the request structure. The flaw enables attackers to bypass security rules that are typically enforced by mod_security, potentially allowing malicious content to reach backend PHP applications without detection. The vulnerability is particularly concerning because it directly impacts the integrity of web application firewalls that organizations rely upon to protect against common web attacks such as SQL injection, cross-site scripting, and file inclusion exploits.
The technical implementation of this vulnerability occurs within the multipart request parsing logic of mod_security2. When processing multipart form data, the module fails to properly validate the structure of individual parts within the request. An attacker can construct a malicious multipart request where an invalid or malformed part appears before the actual data payload. This invalid part causes the parsing mechanism to skip over validation checks that would normally occur, allowing subsequent parts containing malicious content to bypass security controls. The flaw specifically affects how mod_security handles the boundary delimiters and part boundaries within multipart requests, creating a parsing gap that can be exploited to circumvent rule enforcement. This behavior aligns with CWE-129, which describes improper validation of input boundaries, and demonstrates how flawed input processing can lead to security control bypass.
The operational impact of this vulnerability extends beyond simple rule bypass, as it enables attackers to deliver arbitrary POST data to PHP applications that would otherwise be blocked by security rules. This capability allows for exploitation of various attack vectors including but not limited to file upload vulnerabilities, command injection, and data manipulation attacks. The vulnerability is particularly dangerous in environments where mod_security is configured with strict security rules designed to prevent malicious uploads or parameter tampering. Attackers can leverage this flaw to upload malicious files, inject commands, or manipulate application behavior in ways that would normally be prevented by the web application firewall. The attack requires minimal privileges and can be executed through standard HTTP POST requests, making it accessible to threat actors with basic web exploitation knowledge.
Organizations affected by this vulnerability should prioritize immediate mitigation through updating to mod_security2 version 2.7.0 or later, which contains the necessary patches to address the multipart request parsing issue. Additionally, administrators should implement additional defensive measures including monitoring for unusual multipart request patterns, implementing more robust input validation at the application layer, and conducting regular security assessments of their web application firewall configurations. The vulnerability demonstrates the importance of proper input validation and boundary checking in security systems, as outlined in ATT&CK technique T1190 for exploiting vulnerabilities in web applications. Security teams should also consider implementing network-level monitoring to detect anomalous multipart request patterns that may indicate exploitation attempts, and establish incident response procedures to address potential compromise of web applications protected by vulnerable mod_security configurations.