CVE-2003-0789 in HTTP Server
Summary
by MITRE
mod_cgid in Apache before 2.0.48, when using a threaded MPM, does not properly handle CGI redirect paths, which could cause Apache to send the output of a CGI program to the wrong client.
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Analysis
by VulDB Data Team • 08/12/2025
The vulnerability identified as CVE-2003-0789 affects the mod_cgid module in Apache HTTP Server versions prior to 2.0.48 when operating with threaded Multi-Processing Modules. This flaw represents a critical security issue that undermines the fundamental integrity of client-server communication within the web server infrastructure. The vulnerability specifically manifests when Apache processes CGI requests through threaded MPM configurations, creating a scenario where output routing becomes mismanaged between concurrent client connections.
The technical root cause of this vulnerability lies in the improper handling of CGI redirect paths within the mod_cgid module. When threaded MPM is enabled, Apache maintains multiple threads to handle concurrent requests, and the mod_cgid module fails to correctly associate CGI output with the appropriate client connection. This misassociation occurs during the processing of redirect paths in CGI scripts, where the module's internal state management becomes corrupted or inconsistent across threads. The flaw essentially allows Apache to deliver the output of one CGI program to a different client than intended, creating a cross-client data leakage scenario that violates core security principles of process isolation and request confidentiality.
The operational impact of this vulnerability extends beyond simple data leakage to encompass potential information disclosure and service disruption. An attacker could exploit this weakness to obtain sensitive information that should be restricted to specific clients, potentially accessing data belonging to other users connected to the same server instance. This cross-contamination of CGI output could expose session data, authentication tokens, or other confidential information processed by CGI applications. The vulnerability particularly affects environments where multiple concurrent users access CGI-enabled resources, making it especially dangerous in shared hosting environments or multi-tenant web server configurations where isolation between clients is paramount.
From a cybersecurity perspective, this vulnerability aligns with CWE-200, which addresses improper information exposure, and represents a classic case of information leakage through incorrect resource handling. The flaw also intersects with ATT&CK technique T1059.007 for CGI script execution and T1566 for malicious code delivery through web applications. Organizations utilizing Apache with threaded MPM configurations face significant risk from this vulnerability, as it can be exploited without requiring elevated privileges or specialized knowledge beyond basic web application attack techniques. The vulnerability essentially creates a backdoor for data interception that could be leveraged to compromise user sessions, steal sensitive business information, or facilitate further attacks within the compromised server environment.
The recommended mitigation strategy involves upgrading to Apache HTTP Server version 2.0.48 or later, which contains the necessary patches to resolve the mod_cgid threading issue. Additionally, administrators should consider implementing alternative MPM configurations that do not utilize threading for CGI processing, or deploy additional network-level controls to monitor and restrict CGI traffic patterns. Organizations should also conduct thorough security assessments of their CGI applications to identify potential exploitation vectors and ensure proper input validation and output sanitization practices are implemented. Regular security auditing of web server configurations and continuous monitoring of system logs for anomalous CGI execution patterns remain essential defensive measures against this and similar vulnerabilities.