CVE-2013-4352 in HTTP Server
Summary
by MITRE
The cache_invalidate function in modules/cache/cache_storage.c in the mod_cache module in the Apache HTTP Server 2.4.6, when a caching forward proxy is enabled, allows remote HTTP servers to cause a denial of service (NULL pointer dereference and daemon crash) via vectors that trigger a missing hostname value.
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Analysis
by VulDB Data Team • 02/09/2022
The vulnerability identified as CVE-2013-4352 represents a critical denial of service weakness within the Apache HTTP Server 2.4.6 mod_cache module when operating in caching forward proxy mode. This flaw manifests through a NULL pointer dereference condition that occurs when the cache_invalidate function processes requests containing missing hostname values. The issue specifically affects systems configured with caching forward proxy functionality, where Apache acts as an intermediary caching server for client requests. The vulnerability stems from inadequate input validation within the cache storage module, particularly when handling HTTP responses that lack proper hostname identification. When remote HTTP servers send malformed requests that omit hostname information, the mod_cache module fails to properly handle this edge case, resulting in a daemon crash and complete service disruption. This represents a classic example of insufficient error handling and input validation that can be exploited by malicious actors to systematically disrupt web services.
The technical implementation of this vulnerability resides in the cache_storage.c file within the mod_cache module, where the cache_invalidate function lacks proper null checking mechanisms for hostname values. When a caching forward proxy receives an HTTP request with missing hostname data, the function attempts to dereference a NULL pointer during cache invalidation operations, leading to an immediate crash of the Apache daemon process. This type of vulnerability aligns with CWE-476, which specifically addresses NULL pointer dereference conditions in software implementations. The flaw demonstrates poor defensive programming practices where the code assumes the presence of valid hostname data without proper validation checks. The vulnerability is particularly dangerous because it can be triggered remotely by any HTTP server that chooses to send malformed requests to the vulnerable Apache instance, making it an attractive target for denial of service attacks that can effectively shut down web services.
The operational impact of CVE-2013-4352 extends beyond simple service disruption to encompass broader system reliability and availability concerns for organizations relying on Apache HTTP Server with caching forward proxy configurations. When exploited, this vulnerability can cause cascading failures in web infrastructure, particularly affecting high-traffic websites and applications that depend on caching mechanisms for performance optimization. The daemon crash results in immediate unavailability of the web service until manual intervention or automatic restart procedures are initiated, creating potential for significant business disruption. Organizations using Apache in caching proxy roles face particular risk as this vulnerability can be exploited without authentication or specialized privileges, making it accessible to any attacker with network access to the vulnerable server. The attack vector is straightforward and requires minimal technical expertise, which increases the probability of exploitation in real-world scenarios and makes it a preferred target for automated attack tools.
Mitigation strategies for CVE-2013-4352 focus on both immediate patching and operational security measures to reduce exposure. The primary solution involves upgrading to Apache HTTP Server versions that contain the fix for this vulnerability, specifically versions 2.4.7 and later which address the NULL pointer dereference issue. Organizations should also implement network-level protections such as firewall rules that restrict access to caching proxy functionality to trusted sources only, and configure proper input validation at the network perimeter. Additionally, implementing monitoring and alerting systems that can detect unusual patterns of cache invalidation requests may help identify exploitation attempts before they cause service disruption. Security teams should consider disabling caching forward proxy functionality entirely if it is not essential to their operations, as this eliminates the attack surface associated with this specific vulnerability. The remediation process should also include comprehensive testing of updated configurations to ensure that the patch does not introduce compatibility issues with existing caching policies or application requirements, aligning with best practices from the ATT&CK framework for defending against denial of service attacks through proper system hardening and patch management procedures.