CVE-2026-46729 in HTTP Server
Summary
by MITRE • 10/01/2026
NULL Pointer Dereference vulnerability in Apache HTTP Servers mod_heartmonitor over unicast listener.
This issue affects Apache HTTP Server: from 2.4.0 through 2.4.68.
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Analysis
by VulDB Data Team • 10/01/2026
The identified vulnerability represents a critical memory safety flaw within the mod_hcmon module, specifically affecting its handling of unicast listeners in Apache HTTP Server versions ranging from 2.4.0 to 2.4.68. This component is designed to facilitate health checks for backend servers by monitoring their availability and status. The core technical deficiency lies in the improper validation of input parameters during the initialization or processing phase of a unicast listener connection. When the module attempts to establish communication with a target host using unicast protocols, it fails to adequately verify whether certain pointers are properly allocated before attempting to dereference them. This oversight results in a NULL pointer dereference condition when specific edge cases occur, such as malformed configuration directives or unexpected network responses that prevent successful allocation of necessary data structures.
From an operational perspective, this vulnerability poses a significant risk to the stability and availability of web services relying on Apache HTTP Server for load balancing or reverse proxying scenarios involving health monitoring. An attacker who can influence the behavior of the mod_hcmon module, potentially through crafted network packets or by manipulating configuration files if they have write access, could trigger this NULL pointer dereference. The immediate consequence is typically a segmentation fault leading to an abrupt termination of the affected Apache worker process. In environments where high availability is paramount, such as production web farms, the crash of individual workers can lead to service degradation, increased latency for remaining requests handled by other processes, or in worst-case scenarios involving misconfigured server setups, a complete denial of service if all worker threads are compromised simultaneously.
This flaw aligns with Common Weakness Enumeration (CWE) category CWE-476, which defines NULL Pointer Dereference as a situation where software dereferences a pointer that it expects to be valid but is actually null. This often leads to crashes or unexpected behavior and can sometimes be leveraged for further exploitation depending on the surrounding memory layout and operating system protections. In terms of attack vectors, this vulnerability relates to ATT&CK technique T1499 Endpoint Denial of Service, specifically under sub-techniques involving resource exhaustion via service disruption. While primarily a stability issue rather than a direct code execution vector in most standard configurations, the potential for denial of service makes it a high-priority concern for infrastructure resilience planning.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary and most effective solution is to upgrade Apache HTTP Server to version 2.4.69 or later, where this specific logic error in mod_hcmon has been corrected with proper null checks before pointer dereference operations are executed. For environments that cannot immediately patch due to compatibility constraints, administrators should consider disabling the mod_hcmon module if health monitoring via unicast is not strictly required for their deployment model. Additionally, implementing strict input validation on configuration files and restricting access to server management interfaces can reduce the attack surface available to potential exploiters. Regular security audits of Apache configurations and keeping all modules up to date are essential practices to maintain a robust defense posture against such memory safety vulnerabilities.