CVE-2007-3303 in HTTP Server
Summary
by MITRE
Apache httpd 2.0.59 and 2.2.4, with the Prefork MPM module, allows local users to cause a denial of service via certain code sequences executed in a worker process that (1) stop request processing by killing all worker processes and preventing creation of replacements or (2) hang the system by forcing the master process to fork an arbitrarily large number of worker processes. NOTE: This might be an inherent design limitation of Apache with respect to worker processes in hosted environments.
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Analysis
by VulDB Data Team • 07/25/2019
The vulnerability described in CVE-2007-3303 represents a critical denial of service flaw within the Apache HTTP Server versions 2.0.59 and 2.2.4 when configured with the Prefork Multi-Processing Module. This issue stems from how the server handles specific code sequences executed within worker processes, creating a fundamental weakness in the process management architecture that can be exploited by local attackers to disrupt service availability. The vulnerability is particularly concerning because it affects the core process management functionality of Apache, which is widely deployed across web hosting environments and enterprise infrastructure.
The technical flaw manifests through two distinct attack vectors that leverage the Prefork MPM's process handling mechanisms. The first vector involves code sequences that terminate all active worker processes, effectively stopping request processing entirely and preventing the master process from creating replacement worker processes to handle incoming requests. This creates an immediate service disruption where the web server becomes completely unresponsive to client requests. The second vector exploits the master process's forking behavior by forcing it to create an arbitrarily large number of worker processes, leading to system resource exhaustion and potential system hang conditions. These attack methods directly target the fundamental architecture of Apache's process management model, where the master process spawns and manages worker processes to handle concurrent requests.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader system stability concerns, particularly in hosted environments where Apache serves as a critical component of web infrastructure. When exploited, the vulnerability can cause complete service outages that affect multiple websites and applications hosted on the same server, potentially resulting in significant business disruption and customer impact. The inherent design limitation highlighted in the CVE description suggests that this vulnerability is not merely a bug but represents a fundamental architectural weakness in how Apache handles process management under certain conditions, making it particularly challenging to remediate without architectural changes. Organizations relying on Apache with Prefork MPM in production environments face substantial risk from this vulnerability, as it can be exploited by local users with minimal privileges to cause maximum disruption.
The vulnerability aligns with CWE-400, which addresses "Uncontrolled Resource Consumption," and demonstrates characteristics consistent with ATT&CK technique T1499.004, "Endpoint Denial of Service," where adversaries target system resources to prevent normal operation. Mitigation strategies should focus on implementing proper access controls to prevent unauthorized local users from executing malicious code sequences, upgrading to newer Apache versions that address these architectural issues, and configuring appropriate resource limits to prevent excessive process creation. Additionally, organizations should consider alternative MPM modules such as Worker or Event MPM, which handle process management differently and may be less susceptible to this specific class of denial of service attacks. The vulnerability underscores the importance of understanding the underlying architecture of web servers and the potential security implications of process management design decisions in hosted environments.