CVE-2012-1181 in HTTP Server
Summary
by MITRE
fcgid_spawn_ctl.c in the mod_fcgid module 2.3.6 for the Apache HTTP Server does not recognize the FcgidMaxProcessesPerClass directive for a virtual host, which makes it easier for remote attackers to cause a denial of service (memory consumption) via a series of HTTP requests that triggers a process count higher than the intended limit.
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Analysis
by VulDB Data Team • 03/22/2021
The vulnerability identified as CVE-2012-1181 resides within the mod_fcgid module version 2.3.6 of the Apache HTTP Server, specifically in the fcgid_spawn_ctl.c component. This flaw represents a critical configuration oversight that undermines the intended security controls for managing FastCGI process execution. The mod_fcgid module serves as a bridge between Apache and FastCGI applications, enabling dynamic content processing through persistent processes. When properly configured, administrators can control resource consumption through directives like FcgidMaxProcessesPerClass, which limits the number of processes spawned for specific application classes within virtual host contexts.
The technical flaw manifests when the mod_fcgid module fails to properly recognize or enforce the FcgidMaxProcessesPerClass directive at the virtual host level. This directive is designed to prevent unlimited process creation by establishing per-class limits that apply to individual virtual hosts. When this directive is ignored, attackers can exploit the absence of process counting controls to trigger excessive process creation. The vulnerability operates through a carefully crafted sequence of HTTP requests that systematically increment process counts beyond the intended administrative limits, ultimately leading to memory exhaustion and service disruption.
The operational impact of this vulnerability extends beyond simple denial of service, creating a pathway for resource exhaustion attacks that can severely impact server availability and performance. Remote attackers can leverage this flaw to consume excessive system memory and CPU resources through relatively simple HTTP request patterns, effectively rendering the affected web server unable to serve legitimate requests. This vulnerability particularly affects environments where multiple virtual hosts operate with varying resource requirements, as the lack of per-virtual-host process limits allows attackers to target specific virtual host configurations and bypass intended resource controls. The flaw essentially undermines the fundamental principle of resource isolation that should exist between different virtual host contexts.
The vulnerability aligns with CWE-264, which addresses permissions, privileges, and access controls, as it represents a failure in proper access control enforcement within the web server configuration. Additionally, this weakness can be categorized under ATT&CK technique T1499.004, specifically for network denial of service, as it enables attackers to consume network and system resources to prevent legitimate service access. The flaw also relates to CWE-770, which covers allocation of resources without limits or throttling, demonstrating how inadequate resource management can lead to system instability. Organizations should implement immediate mitigations including upgrading to patched versions of mod_fcgid, implementing proper process limit configurations, and monitoring for unusual process creation patterns. The vulnerability underscores the critical importance of proper directive enforcement in web server configurations and highlights the need for comprehensive security testing of module behaviors under various configuration scenarios to prevent such resource exhaustion attacks.