CVE-2009-4017 in PHP
Summary
by MITRE
PHP before 5.2.12 and 5.3.x before 5.3.1 does not restrict the number of temporary files created when handling a multipart/form-data POST request, which allows remote attackers to cause a denial of service (resource exhaustion), and makes it easier for remote attackers to exploit local file inclusion vulnerabilities, via multiple requests, related to lack of support for the max_file_uploads directive.
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Analysis
by VulDB Data Team • 01/31/2025
The vulnerability identified as CVE-2009-4017 represents a critical resource management flaw in php versions prior to 5.2.12 and 5.3.1, specifically affecting the handling of multipart/form-data POST requests. This issue stems from the absence of proper limitations on temporary file creation during file upload processing, creating a scenario where malicious actors can exploit the system's lack of safeguards to exhaust available resources. The vulnerability operates within the context of web application security where file upload functionalities are commonly utilized, making it particularly dangerous in production environments where resource constraints can severely impact system availability and performance.
The technical implementation of this vulnerability involves the PHP engine's processing of HTTP POST requests containing multipart/form-data content, which is the standard format used for file uploads in web applications. When PHP receives such requests without proper configuration limits, it creates temporary files for each uploaded file in the system's temporary directory. The absence of a max_file_uploads directive means that there is no cap on how many temporary files can be created during a single request or across multiple requests, allowing attackers to continuously submit requests with numerous file parameters. This flaw aligns with CWE-400, which categorizes resource exhaustion vulnerabilities, and specifically relates to improper resource management where the system fails to enforce reasonable limits on resource consumption.
The operational impact of CVE-2009-4017 extends beyond simple denial of service conditions to create significant security risks that compound the primary resource exhaustion threat. Attackers can leverage this vulnerability to consume all available disk space in the temporary directory, leading to system instability and potential crashes of the web server or application itself. The resource exhaustion creates an environment where legitimate users cannot upload files, and the system may become unresponsive or crash entirely. Additionally, this vulnerability enables attackers to more easily exploit local file inclusion vulnerabilities by filling up the temporary file system, which can be particularly dangerous in applications that rely on temporary files for processing or storage. From an adversarial perspective, this vulnerability maps to several ATT&CK techniques including resource exhaustion and privilege escalation through system manipulation.
The exploitation of this vulnerability requires minimal technical sophistication, making it particularly dangerous as it can be automated and used in large-scale attacks. Attackers can craft malicious POST requests containing hundreds or thousands of file parameters, each creating a temporary file that consumes disk space and system resources. The cumulative effect of multiple such requests can quickly exhaust available storage space, causing cascading failures in the web application infrastructure. Organizations running affected PHP versions face significant risk of service disruption, potential data loss, and increased vulnerability to additional attack vectors that exploit the compromised system state. The vulnerability particularly affects web applications that accept file uploads without proper input validation and resource limiting, making it a widespread concern across many web server implementations.
Mitigation strategies for CVE-2009-4017 primarily involve upgrading to patched PHP versions where the max_file_uploads directive is properly supported and implemented. System administrators should also configure appropriate limits on temporary file creation through php.ini settings, specifically implementing the max_file_uploads directive to restrict the maximum number of files that can be uploaded simultaneously. Additionally, organizations should implement monitoring of temporary file directories to detect unusual resource consumption patterns and establish automated alerts for potential exploitation attempts. Network-level mitigations can include implementing rate limiting on file upload endpoints and configuring firewalls to restrict the number of concurrent upload requests from single IP addresses. The implementation of proper input validation and sanitization measures should also be enforced to prevent malicious file uploads from being processed, and regular security audits should be conducted to ensure that all PHP configurations properly enforce resource limits and prevent exploitation of this vulnerability.