CVE-2012-3502 in HTTP Server
Summary
by MITRE
The proxy functionality in (1) mod_proxy_ajp.c in the mod_proxy_ajp module and (2) mod_proxy_http.c in the mod_proxy_http module in the Apache HTTP Server 2.4.x before 2.4.3 does not properly determine the situations that require closing a back-end connection, which allows remote attackers to obtain sensitive information in opportunistic circumstances by reading a response that was intended for a different client.
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Analysis
by VulDB Data Team • 04/12/2021
The vulnerability described in CVE-2012-3502 resides within the Apache HTTP Server's proxy functionality, specifically affecting versions 2.4.x prior to 2.4.3. This issue impacts two critical modules: mod_proxy_ajp.c and mod_proxy_http.c which handle AJP and HTTP proxy operations respectively. The flaw represents a significant security weakness that undermines the fundamental principle of client isolation in proxy server operations, creating potential for information disclosure attacks.
The technical root cause of this vulnerability lies in the improper determination of when backend connections should be closed within the proxy modules. When Apache processes proxy requests, it maintains connections to backend servers to improve performance through connection reuse. However, the flawed logic in these modules fails to correctly assess scenarios where connection closure is necessary, particularly when handling responses that may be delivered to the wrong client. This mismanagement occurs during the processing of proxy responses where the server does not adequately validate or manage the connection state transitions, leading to potential cross-contamination of response data between different client sessions.
The operational impact of this vulnerability creates a scenario where remote attackers can exploit opportunistic conditions to access sensitive information that was intended for other clients. This occurs when the proxy server fails to properly close or reset connections between backend servers and the client, allowing response data from one client session to be inadvertently read by another client. The vulnerability is particularly concerning because it operates under opportunistic circumstances, meaning attackers do not need to exploit specific conditions but can take advantage of the inherent flaws in connection management during normal proxy operations.
This vulnerability aligns with CWE-200, which addresses "Information Exposure," and represents a classic case of improper resource management in network services. The flaw also relates to ATT&CK technique T1071.004, "Application Layer Protocol: DNS," and T1566.001, "Phishing: Spearphishing Attachment," as it can enable attackers to harvest sensitive data through proxy server operations that may be used in broader attack chains. The issue particularly affects organizations using Apache HTTP Server as a reverse proxy or load balancer, where multiple clients connect through the same proxy server to different backend services.
The exploitation of this vulnerability requires minimal privileges and can be executed remotely, making it particularly dangerous in environments where Apache serves as a critical component of web infrastructure. Organizations that rely on proxy functionality for application delivery, load balancing, or security filtering are at risk, especially those handling sensitive data such as financial transactions, personal information, or corporate data. The vulnerability demonstrates a critical flaw in connection state management that can persist across multiple concurrent client sessions, potentially allowing attackers to accumulate sensitive information over time.
Mitigation strategies should focus on immediate patching of affected Apache HTTP Server versions to 2.4.3 or later, which contains the necessary fixes for proper connection state management. Additionally, organizations should implement network segmentation and access controls to limit exposure, monitor proxy server logs for unusual connection patterns, and consider implementing additional logging mechanisms to detect potential information leakage events. Security teams should also review proxy configurations to ensure proper connection handling and consider implementing more robust connection pooling strategies that minimize the risk of cross-client response contamination. The fix addresses the core issue by implementing proper connection state validation and ensuring that backend connections are appropriately closed when required to maintain client isolation and prevent response data leakage between different client sessions.