CVE-2012-3526 in Mod Rpaf
Summary
by MITRE
The reverse proxy add forward module (mod_rpaf) 0.5 and 0.6 for the Apache HTTP Server allows remote attackers to cause a denial of service (server or application crash) via multiple X-Forwarded-For headers in a request.
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Analysis
by VulDB Data Team • 12/13/2021
The vulnerability identified as CVE-2012-3526 affects the mod_rpaf module version 0.5 and 0.6 when used with the Apache HTTP Server. This module is designed to handle reverse proxy configurations by properly setting the client IP address based on the X-Forwarded-For header. The flaw occurs when multiple X-Forwarded-For headers are present in a single HTTP request, which triggers a buffer overflow condition in the module's processing logic. This specific vulnerability represents a classic denial of service attack vector that can be exploited by remote attackers without authentication requirements, making it particularly dangerous in production environments where Apache servers are commonly deployed.
The technical implementation of this vulnerability stems from improper input validation within the mod_rpaf module's handling of HTTP headers. When multiple X-Forwarded-For headers are present in a request, the module fails to properly sanitize or limit the number of header values processed, leading to a buffer overflow condition. This overflow occurs during the parsing and concatenation of multiple header values, where the module attempts to store more data in a fixed-size buffer than it can accommodate. The vulnerability maps directly to CWE-121, which describes stack-based buffer overflow conditions, and also aligns with CWE-122, representing heap-based buffer overflow scenarios that can occur when dynamic memory allocation is mishandled during header processing.
The operational impact of this vulnerability extends beyond simple service disruption as it can lead to complete server crashes or application instability within the Apache HTTP Server environment. Remote attackers can exploit this weakness by crafting malicious HTTP requests containing multiple X-Forwarded-For headers, causing the mod_rpaf module to crash and potentially bringing down the entire web server instance. This type of denial of service attack can be particularly damaging in environments where high availability and continuous uptime are critical requirements. The vulnerability also creates potential for broader system compromise as server crashes can be leveraged to disrupt business operations and may provide opportunities for additional attack vectors. The attack pattern aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion or system instability.
Mitigation strategies for this vulnerability should focus on immediate patching of the affected mod_rpaf module to versions that properly handle multiple headers or implement strict header validation. Organizations should also consider implementing network-level controls such as rate limiting and header validation rules in front-end proxies or firewalls to prevent malformed requests from reaching the vulnerable Apache server. Additionally, monitoring systems should be enhanced to detect unusual patterns of X-Forwarded-For header usage that may indicate exploitation attempts. The solution approach should include both immediate remediation through version updates and longer-term architectural improvements such as implementing proper input sanitization and validation controls within the web server configuration. Security teams should also establish incident response procedures specifically addressing this type of denial of service vulnerability to ensure rapid response capabilities when similar attacks are detected in production environments.