CVE-2002-0839 in HTTP Server
Summary
by MITRE
The shared memory scoreboard in the HTTP daemon for Apache 1.3.x before 1.3.27 allows any user running as the Apache UID to send a SIGUSR1 signal to any process as root, resulting in a denial of service (process kill) or possibly other behaviors that would not normally be allowed, by modifying the parent[].pid and parent[].last_rtime segments in the scoreboard.
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Analysis
by VulDB Data Team • 05/09/2019
The vulnerability described in CVE-2002-0839 represents a critical privilege escalation flaw within the Apache HTTP Server 1.3.x series prior to version 1.3.27. This issue resides in the shared memory scoreboard mechanism that Apache employs to track child processes and their status information. The scoreboard functionality is designed to facilitate communication between the parent Apache process and its child worker processes, enabling monitoring and management of the server's operational state. However, the implementation contains a fundamental flaw in how it handles process identification and signal handling within the shared memory segments.
The technical exploitation of this vulnerability stems from improper access control mechanisms within the scoreboard's shared memory regions. Specifically, when Apache operates with elevated privileges, it creates shared memory segments that contain process identification information including parent[].pid and parent[].last_rtime fields. These segments are accessible to any user running under the Apache user ID, which typically operates with limited privileges but still maintains access to the shared memory space. The flaw allows an attacker to directly modify these memory segments, effectively manipulating the process identifiers that the server uses to determine which processes to signal with SIGUSR1.
This vulnerability operates under the Common Weakness Enumeration framework as CWE-264, representing "Permissions, Privileges, and Access Controls" weaknesses where insufficient access control mechanisms allow unauthorized users to manipulate system resources. The attack vector specifically aligns with CWE-276, "Improper Ownership", since the shared memory segments are not properly secured against modification by processes running under the same user context as the Apache daemon. The operational impact of this vulnerability extends beyond simple denial of service scenarios, as demonstrated by the potential for "possibly other behaviors that would not normally be allowed" which could include arbitrary process manipulation or privilege escalation.
The security implications of this vulnerability are severe and can be mapped to multiple techniques within the MITRE ATT&CK framework, particularly under the "Privilege Escalation" and "Defense Evasion" domains. The technique falls under T1068, "Exploitation for Privilege Escalation", where attackers leverage system vulnerabilities to gain higher privileges than initially granted. Additionally, the vulnerability enables T1059, "Command and Scripting Interpreter", through the ability to send signals to processes, potentially allowing for more sophisticated attack chains. The shared memory manipulation technique also relates to T1070, "Indicator Removal on Host", as the attacker could potentially hide their activities by manipulating process tracking information.
The impact of this vulnerability extends to system availability and integrity, as the ability to send SIGUSR1 signals to any process as root creates opportunities for both denial of service attacks and potential system compromise. While the immediate effect may appear to be simple process termination, the underlying flaw demonstrates a broader architectural weakness in how Apache manages shared resources and process communication. Organizations running vulnerable Apache versions face significant risk of service disruption and potential unauthorized access to system resources, particularly in environments where the Apache user ID has access to critical system processes.
Mitigation strategies for this vulnerability require immediate patching of affected Apache installations to version 1.3.27 or later, where the shared memory access controls have been properly implemented. System administrators should also implement proper process isolation and privilege separation mechanisms, ensuring that the Apache user ID has minimal access to system processes beyond what is necessary for web service operation. Additionally, monitoring for unauthorized modifications to shared memory segments and implementing proper access control lists for shared memory regions can help detect and prevent exploitation attempts. The vulnerability highlights the importance of proper memory management and access control in multi-process server applications, emphasizing the need for thorough security reviews of shared resource handling in system-level software components.