CVE-2007-1863 in Mac OS X Server
Summary
by MITRE
cache_util.c in the mod_cache module in Apache HTTP Server (httpd), when caching is enabled and a threaded Multi-Processing Module (MPM) is used, allows remote attackers to cause a denial of service (child processing handler crash) via a request with the (1) s-maxage, (2) max-age, (3) min-fresh, or (4) max-stale Cache-Control headers without a value.
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Analysis
by VulDB Data Team • 07/21/2019
The vulnerability identified as CVE-2007-1863 represents a critical denial of service weakness within the Apache HTTP Server's mod_cache module, specifically affecting configurations that utilize threaded Multi-Processing Modules. This flaw manifests when the server processes HTTP requests containing specific Cache-Control headers without associated values, creating a scenario where child processes handling these requests become unstable and crash. The issue directly impacts the server's ability to maintain consistent service availability, particularly in high-traffic environments where caching mechanisms are actively employed to optimize performance. The vulnerability stems from inadequate input validation within the cache_util.c component, which fails to properly handle malformed Cache-Control directives that lack required parameter values.
The technical exploitation of this vulnerability occurs through the manipulation of HTTP Cache-Control headers in incoming requests, specifically targeting s-maxage, max-age, min-fresh, and max-stale parameters when they appear without accompanying values. When Apache's mod_cache module encounters these malformed headers during request processing, the cache_util.c function attempts to parse and handle the parameters without proper bounds checking or validation, leading to memory corruption or null pointer dereference conditions. This processing error causes the child worker process to terminate unexpectedly, resulting in a denial of service condition that can be amplified through repeated exploitation. The vulnerability is particularly dangerous in threaded environments because the crash of individual child processes can disrupt the entire server's ability to handle concurrent requests, potentially causing cascading failures throughout the web server infrastructure.
From an operational impact perspective, this vulnerability creates significant security and reliability concerns for Apache HTTP Server deployments, especially those configured with threaded MPMs such as worker or event MPMs. The denial of service attack can be executed remotely without authentication requirements, making it an attractive target for malicious actors seeking to disrupt web services. The vulnerability's exploitation directly violates the principle of least privilege and can lead to unauthorized service disruption, potentially affecting business continuity and user access to web applications. Organizations utilizing Apache servers with caching enabled are particularly at risk, as the vulnerability can be triggered by simply sending crafted HTTP requests containing the specific Cache-Control headers without values, requiring minimal technical expertise to execute successfully.
Mitigation strategies for CVE-2007-1863 should focus on immediate patching of affected Apache installations to the latest security releases that address the input validation issues in the mod_cache module. System administrators should also implement network-level controls such as web application firewalls that can detect and block requests containing malformed Cache-Control headers, providing an additional layer of defense. Configuration adjustments including disabling the mod_cache module when not required, or implementing more restrictive cache policies that prevent processing of untrusted Cache-Control directives, can serve as temporary workarounds. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks, emphasizing the importance of proper input sanitization and robust error handling in web server implementations. Regular security auditing of HTTP server configurations and monitoring for unusual process termination patterns should be implemented to detect potential exploitation attempts and maintain overall system resilience against such vulnerabilities.