CVE-2008-2364 in HTTP Server
Summary
by MITRE
The ap_proxy_http_process_response function in mod_proxy_http.c in the mod_proxy module in the Apache HTTP Server 2.0.63 and 2.2.8 does not limit the number of forwarded interim responses, which allows remote HTTP servers to cause a denial of service (memory consumption) via a large number of interim responses.
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Analysis
by VulDB Data Team • 08/11/2019
The vulnerability identified as CVE-2008-2364 resides within the Apache HTTP Server's mod_proxy module, specifically in the ap_proxy_http_process_response function located in mod_proxy_http.c. This flaw manifests in Apache versions 2.0.63 and 2.2.8 where the proxy module fails to impose reasonable limits on the number of interim HTTP responses that can be forwarded to clients. Interim responses, typically HTTP status codes 100 through 101, are designed to indicate that the server has received the request headers and is processing the request, but these responses are not intended to be forwarded to clients in unlimited quantities. The absence of rate limiting or maximum threshold controls allows malicious or compromised HTTP servers to flood the proxy with numerous interim responses, creating a memory exhaustion condition that can lead to system instability and denial of service.
This vulnerability represents a classic example of resource exhaustion attack patterns that align with CWE-400, which catalogs weaknesses related to uncontrolled resource consumption. The flaw operates by exploiting the proxy server's lack of defensive mechanisms against excessive response forwarding, creating a scenario where memory allocated for processing HTTP responses grows uncontrollably. The operational impact extends beyond simple service disruption as it can consume substantial system resources including memory and CPU cycles, potentially affecting other services running on the same system. This type of vulnerability is particularly dangerous in high-traffic environments where the proxy server acts as a critical infrastructure component handling numerous concurrent requests.
From an adversarial perspective, this vulnerability maps directly to several ATT&CK techniques including T1499.004 for network denial of service and T1595.001 for reconnaissance through information gathering. Attackers can leverage this weakness to perform sustained denial of service attacks against Apache proxy servers without requiring elevated privileges or complex exploitation techniques. The attack vector is straightforward: a remote HTTP server can send an excessive number of interim responses to an Apache proxy, causing the server to consume increasing amounts of memory until system resources are exhausted. The vulnerability is particularly concerning because it can be exploited through legitimate proxy functionality without triggering typical security monitoring mechanisms that might detect more obvious attack patterns.
Mitigation strategies for CVE-2008-2364 should focus on implementing proper response limiting mechanisms within the proxy configuration. System administrators should consider upgrading to patched versions of Apache HTTP Server where this vulnerability has been addressed through the introduction of configurable limits on interim response forwarding. Additionally, implementing proxy server configuration parameters that restrict the number of interim responses allowed per request can provide defense in depth. Network-level mitigations such as implementing rate limiting at the firewall or load balancer level can help prevent excessive interim response flooding. The solution should also include monitoring and alerting mechanisms to detect unusual memory consumption patterns that might indicate exploitation attempts. Organizations should conduct regular security assessments of their proxy configurations to ensure that such resource exhaustion vulnerabilities are properly mitigated and that appropriate access controls are maintained to prevent unauthorized modification of proxy settings.