CVE-2019-10097 in HTTP Server
Summary
by MITRE
In Apache HTTP Server 2.4.32-2.4.39, when mod_remoteip was configured to use a trusted intermediary proxy server using the "PROXY" protocol, a specially crafted PROXY header could trigger a stack buffer overflow or NULL pointer deference. This vulnerability could only be triggered by a trusted proxy and not by untrusted HTTP clients.
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Analysis
by VulDB Data Team • 11/24/2020
The vulnerability identified as CVE-2019-10097 affects the Apache HTTP Server version range 2.4.32 through 2.4.39 and specifically targets the mod_remoteip module when configured to utilize the PROXY protocol for trusted intermediary proxy servers. This security flaw represents a critical issue within the server's handling of network connection metadata, where the server's response to PROXY protocol headers contains a fundamental buffer management error that can lead to system instability and potential exploitation. The vulnerability exists within the processing logic of the mod_remoteip module which is designed to handle forwarded client information from trusted proxy servers, creating a scenario where legitimate proxy configurations can become attack vectors when malformed headers are presented.
The technical implementation of this vulnerability stems from improper bounds checking and memory management within the PROXY protocol header parsing logic of mod_remoteip. When a trusted proxy server sends a PROXY header containing specially crafted data, the server's internal buffer handling mechanism fails to properly validate the header length and content structure. This results in either a stack buffer overflow where malicious data overflows allocated memory space, or a NULL pointer dereference when the system attempts to access memory locations that have not been properly initialized or validated. The vulnerability manifests as a memory corruption issue that can potentially lead to arbitrary code execution or denial of service conditions, depending on how the overflow or dereference is exploited. This flaw aligns with CWE-121, which describes stack-based buffer overflow conditions, and CWE-476, which addresses NULL pointer dereference scenarios.
The operational impact of CVE-2019-10097 is significant within environments that rely on trusted proxy configurations for load balancing, SSL termination, or application gateway functions. Since the vulnerability requires a trusted proxy to be present and active, it cannot be exploited by external untrusted clients, making it more of an internal security concern than a direct internet-facing vulnerability. However, this limitation does not reduce its severity as organizations often trust their internal proxy infrastructure, and compromise of a single trusted proxy server could provide an attacker with a pathway to execute malicious code on the Apache server. The vulnerability affects systems where mod_remoteip is enabled and configured to process PROXY protocol headers, which is common in cloud environments, microservices architectures, and enterprise network topologies that utilize proxy-based traffic management. Organizations using Apache HTTP Server in production environments with proxy configurations are particularly at risk.
Mitigation strategies for CVE-2019-10097 should prioritize immediate patching of affected Apache HTTP Server installations to versions that contain the necessary fixes for the buffer overflow and NULL pointer dereference conditions. System administrators should also implement strict access controls and monitoring around proxy server configurations to limit the potential attack surface, as the vulnerability requires a trusted proxy to be active. The recommended approach includes validating all PROXY protocol headers received from intermediaries, implementing rate limiting and header size restrictions, and conducting thorough security audits of all proxy server configurations. Additionally, organizations should consider disabling mod_remoteip when PROXY protocol headers are not strictly necessary, and implementing network segmentation to isolate critical Apache servers from potentially compromised proxy infrastructure. This vulnerability demonstrates the importance of maintaining strict input validation for all network-facing components and aligns with ATT&CK technique T1059, which covers command and script injection, as the exploitation could potentially lead to remote code execution through memory corruption. Organizations should also implement comprehensive logging and monitoring to detect anomalous PROXY header patterns that might indicate exploitation attempts, as the vulnerability's exploitation would likely generate unusual network traffic patterns or system behavior that could be detected through proper security monitoring.