CVE-2009-3622 in WordPress
Summary
by MITRE
Algorithmic complexity vulnerability in wp-trackback.php in WordPress before 2.8.5 allows remote attackers to cause a denial of service (CPU consumption and server hang) via a long title parameter in conjunction with a charset parameter composed of many comma-separated "UTF-8" substrings, related to the mb_convert_encoding function in PHP.
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Analysis
by VulDB Data Team • 12/22/2024
The vulnerability described in CVE-2009-3622 represents a critical algorithmic complexity issue within WordPress version 2.8.4 and earlier, specifically affecting the wp-trackback.php script. This flaw exploits the inherent performance characteristics of PHP's mb_convert_encoding function when processing malformed input parameters. The vulnerability manifests when a remote attacker submits a specially crafted trackback request containing an excessively long title parameter combined with a charset parameter that consists of numerous comma-separated "UTF-8" substrings. This particular combination triggers inefficient processing within the WordPress core codebase, creating a condition where the server's CPU resources become consumed at an exponential rate. The vulnerability operates at the intersection of improper input validation and algorithmic complexity, where the system's response time grows dramatically with input size rather than remaining constant or linear. This type of vulnerability falls under the CWE-1333 category, which specifically addresses algorithmic complexity vulnerabilities, and represents a classic example of a resource exhaustion attack that can effectively bring down web servers through excessive computational overhead.
The technical implementation of this vulnerability leverages PHP's mb_convert_encoding function, which is designed to convert strings between different character encodings. When WordPress processes trackback requests through wp-trackback.php, it utilizes this function to handle charset conversions for incoming data. The flaw occurs because the mb_convert_encoding function exhibits quadratic or worse time complexity when processing large numbers of comma-separated encoding specifications, even when they are identical strings like "UTF-8". The vulnerability specifically targets the parameter parsing logic in WordPress where the charset parameter is processed without adequate bounds checking or input sanitization. The system's response to this malformed input causes the server to enter a computationally intensive loop, consuming CPU cycles and potentially leading to complete server unresponsiveness or denial of service conditions. This behavior aligns with the ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly benign input processing can become a vector for system compromise through resource exhaustion.
The operational impact of CVE-2009-3622 extends beyond simple service disruption to potentially compromise the entire availability of WordPress installations. When exploited, this vulnerability can cause servers to become unresponsive for extended periods, effectively rendering websites inaccessible to legitimate users while attackers maintain their ability to continue the attack. The computational overhead created by this vulnerability can cause servers to consume 100% CPU resources, leading to cascading failures in web application performance and potentially affecting other services running on the same infrastructure. Organizations running vulnerable WordPress installations face significant risk of operational disruption, particularly those with high traffic volumes or limited computational resources where the impact of a single attack can be magnified. The vulnerability affects the core WordPress functionality and impacts all websites using the affected versions, making it a particularly dangerous issue for web hosts and content management system administrators who must address this across multiple installations. The attack vector is particularly concerning because it requires minimal sophistication to execute and can be automated, making it a preferred method for attackers seeking to cause widespread disruption.
Mitigation strategies for CVE-2009-3622 focus primarily on upgrading to WordPress version 2.8.5 or later, which contains the necessary patches to address the algorithmic complexity issue in wp-trackback.php. Additionally, administrators should implement input validation measures that limit the length of title and charset parameters in trackback requests, effectively preventing the exploitation of the vulnerability through parameter manipulation. Network-level protections such as rate limiting and request filtering can help reduce the impact of automated attacks, while server configuration adjustments may include limiting the maximum execution time for PHP processes to prevent complete system hangs. The vulnerability highlights the importance of proper input validation and algorithmic complexity considerations in web application security, particularly for functions that process user-supplied data. Organizations should also implement monitoring systems to detect unusual CPU usage patterns that might indicate exploitation attempts, and maintain current security patches to protect against similar vulnerabilities in the future. The fix implemented in WordPress 2.8.5 specifically addresses the mb_convert_encoding function usage in trackback processing, ensuring that charset parameters are properly validated and normalized before processing, thereby preventing the exponential computational complexity that led to the vulnerability.