CVE-2007-3304 in HTTP Server
Summary
by MITRE
Apache httpd 1.3.37, 2.0.59, and 2.2.4 with the Prefork MPM module, allows local users to cause a denial of service by modifying the worker_score and process_score arrays to reference an arbitrary process ID, which is sent a SIGUSR1 signal from the master process, aka "SIGUSR1 killer."
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Analysis
by VulDB Data Team • 07/21/2019
The vulnerability described in CVE-2007-3304 represents a critical denial of service flaw within the Apache HTTP Server software family, specifically affecting versions 1.3.37, 2.0.59, and 2.2.4 when configured with the Prefork Multi-Processing Module. This issue stems from improper validation of process identifiers within the server's resource management mechanisms, creating a scenario where local attackers can manipulate internal data structures to target arbitrary processes. The flaw operates through the manipulation of worker_score and process_score arrays, which are integral to Apache's process scheduling and resource allocation algorithms. When these arrays are incorrectly modified to reference arbitrary process IDs, the master process subsequently sends SIGUSR1 signals to these targeted processes, potentially causing unexpected behavior or system instability. This vulnerability falls under the category of improper input validation and weak access control mechanisms, aligning with CWE-20, which addresses improper input validation in software systems. The issue is particularly concerning because it allows local users to escalate their privileges and cause system-wide disruptions, representing a significant security risk in multi-user environments where Apache serves as a web server.
The technical implementation of this vulnerability exploits the Prefork MPM's internal process management architecture, where the master process maintains arrays to track worker processes and their performance metrics. These arrays, worker_score and process_score, are designed to help the master process make decisions about process allocation and resource distribution. However, the lack of proper bounds checking and process ID validation allows attackers to inject malicious values into these arrays, effectively redirecting the master process's signaling operations to unintended targets. The SIGUSR1 signal, typically used for process communication and control, becomes a weapon in this attack vector when improperly directed at arbitrary process IDs. This manipulation can lead to processes receiving signals they were not designed to handle, potentially causing crashes, hangs, or other destabilizing behaviors that ultimately result in denial of service conditions. The vulnerability demonstrates a classic example of how internal data structure manipulation can be leveraged to create external security impacts, as described in the ATT&CK framework under the technique of privilege escalation through process manipulation.
The operational impact of CVE-2007-3304 extends beyond simple service disruption, as it represents a fundamental flaw in Apache's process management security model. When exploited, this vulnerability can cause cascading failures within the web server infrastructure, potentially affecting multiple concurrent connections and user sessions. The local nature of the attack means that an attacker must already have access to the system, but this access level is often achievable through various attack vectors such as compromised user accounts or local privilege escalation exploits. The vulnerability's exploitation requires minimal resources and can be automated, making it particularly dangerous in environments where Apache serves as a critical infrastructure component. Organizations running affected versions of Apache are at risk of experiencing service degradation or complete service outages, especially during peak traffic periods when process management is most critical. The vulnerability also highlights the importance of proper input validation and access control mechanisms within server applications, as it demonstrates how insufficient validation of internal data structures can create security weaknesses that attackers can exploit. System administrators should consider this vulnerability as part of their broader security posture assessment, particularly in environments where local access is possible or where multiple users share system resources. The flaw serves as a reminder of the critical importance of maintaining up-to-date software versions and implementing proper security controls to prevent local privilege escalation attacks that can lead to significant operational disruptions.