CVE-2009-1191 in HTTP Server
Summary
by MITRE
mod_proxy_ajp.c in the mod_proxy_ajp module in the Apache HTTP Server 2.2.11 allows remote attackers to obtain sensitive response data, intended for a client that sent an earlier POST request with no request body, via an HTTP request.
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Analysis
by VulDB Data Team • 09/06/2019
The vulnerability described in CVE-2009-1191 affects the mod_proxy_ajp module within the Apache HTTP Server version 2.2.11, representing a critical information disclosure flaw that can be exploited by remote attackers. This vulnerability specifically targets the handling of HTTP requests where a client sends a POST request without a request body, followed by another HTTP request that triggers the exposure of sensitive response data. The issue stems from improper handling of the AJP protocol within the proxy module, which is designed to facilitate communication between Apache and application servers such as Apache Tomcat. The flaw allows attackers to potentially intercept and access sensitive data that should have been isolated for the original client, creating a significant security risk in environments where Apache serves as a proxy for backend application servers.
The technical root cause of this vulnerability lies in the incorrect processing of HTTP request sequences within the mod_proxy_ajp.c module, where the server fails to properly maintain request context separation between different client interactions. When a POST request is sent without a request body, the module's internal state management becomes inconsistent, leading to a scenario where subsequent requests can inadvertently access response data that was intended for a previous client. This behavior violates fundamental security principles of request isolation and data confidentiality, as the proxy module does not properly track or manage the association between specific requests and their corresponding responses. The vulnerability specifically manifests when the AJP protocol is used for communication between Apache and backend servers, making it particularly relevant in environments utilizing mod_proxy_ajp for load balancing or application proxying scenarios.
The operational impact of CVE-2009-1191 extends beyond simple information disclosure, as it can potentially enable attackers to access sensitive user data, session information, or application responses that should remain confidential. This vulnerability is particularly dangerous in web application environments where Apache acts as a reverse proxy or load balancer, as it could allow unauthorized access to data that was originally intended for specific clients. The attack vector requires a remote attacker to send a specific sequence of HTTP requests through the vulnerable proxy module, making it somewhat indirect but still exploitable in production environments. Organizations using Apache HTTP Server with mod_proxy_ajp configured for backend application servers face significant risk of data leakage, potentially exposing user credentials, personal information, or business-critical data that should remain isolated between different client sessions. The vulnerability can be leveraged as part of broader attack chains to escalate privileges or gain deeper access to compromised systems.
Mitigation strategies for CVE-2009-1191 should prioritize immediate patching of affected Apache HTTP Server installations to version 2.2.12 or later, where the vulnerability has been addressed through proper request context management. Organizations should also consider implementing additional network-level controls such as firewall rules to restrict access to the affected proxy endpoints, particularly when AJP protocol is in use. Security teams should conduct comprehensive audits of their Apache configurations to identify and disable unnecessary proxy modules, especially mod_proxy_ajp, when not required for business operations. The vulnerability aligns with CWE-200 (Information Exposure) and can be classified under ATT&CK technique T1566.001 (Phishing via Social Engineering) when combined with other exploitation methods, though the primary impact is information disclosure rather than direct system compromise. Regular security monitoring and log analysis should be implemented to detect anomalous request patterns that might indicate exploitation attempts, while also ensuring that proper access controls are in place to limit who can send requests to the affected proxy endpoints.