CVE-2003-1054 in mod_access_referer
Summary
by MITRE
mod_access_referer 1.0.2 allows remote attackers to cause a denial of service (crash) via a malformed Referer header that is missing a hostname, as parsed by the ap_parse_uri_components function in Apache, which triggers a null dereference.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability described in CVE-2003-1054 represents a critical denial of service flaw within the Apache HTTP Server's mod_access_referer module version 1.0.2. This issue arises from improper handling of HTTP Referer headers during the parsing process, specifically when the header lacks a valid hostname component. The vulnerability is particularly dangerous because it can be exploited remotely by attackers who craft malicious HTTP requests containing malformed Referer headers. The affected component ap_parse_uri_components within Apache's core processing pipeline fails to properly validate the structure of Referer headers before attempting to process them, creating a condition where a null pointer dereference occurs when the system encounters a Referer header missing its hostname portion.
The technical exploitation of this vulnerability occurs when an attacker sends an HTTP request with a Referer header that contains only a scheme and path components without a proper hostname. When Apache's ap_parse_uri_components function processes this malformed header, it attempts to access memory locations that have not been properly initialized or validated. This null dereference condition causes the Apache server process to crash and terminate unexpectedly, leading to a denial of service condition that affects legitimate users attempting to access the web server. The vulnerability specifically targets the URI component parsing logic within Apache's request handling framework, where the absence of hostname validation creates an exploitable path that directly leads to memory access violations.
From an operational standpoint, this vulnerability presents significant risk to web server availability and service continuity. The denial of service impact can be substantial as Apache server processes may crash repeatedly, requiring manual intervention for restart and potentially causing extended downtime. Organizations relying on Apache web servers for critical applications face potential business disruption when this vulnerability is exploited, particularly in environments where automated monitoring and failover systems are not properly configured to handle such service interruptions. The remote nature of the attack means that adversaries can exploit this flaw from anywhere on the internet without requiring local system access or authentication credentials.
Security practitioners should implement multiple layers of mitigation to address this vulnerability effectively. The primary recommendation involves upgrading to Apache versions that contain fixes for the URI parsing logic and have patched the specific null dereference condition in ap_parse_uri_components. Additionally, administrators should consider implementing web application firewalls or intrusion prevention systems that can detect and block malformed Referer headers before they reach the Apache server. Network-level filtering can also be employed to restrict access to the Referer header parsing functionality or to drop requests containing suspicious header patterns. Organizations should also review their Apache configuration to disable the mod_access_referer module if it is not essential for their security policies, as this module was primarily designed for access control based on referer information rather than being a core server component.
This vulnerability aligns with CWE-476 which describes NULL Pointer Dereference conditions in software implementations. The flaw demonstrates how improper input validation can lead to memory corruption issues, making it relevant to the broader category of memory safety vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique related to Network Denial of Service, where adversaries exploit weaknesses in network services to disrupt availability. The attack surface is particularly concerning given that Referer headers are commonly sent by web browsers and are part of standard HTTP protocol behavior, making this a low-effort, high-impact attack vector that can be exploited without specialized tools or deep technical knowledge of the target system.