CVE-2026-23918 in HTTP Server
Summary
by MITRE • 05/04/2026
Double Free and possible RCE vulnerability in Apache HTTP Server with the HTTP/2 protocol.
This issue affects Apache HTTP Server: 2.4.66.
Users are recommended to upgrade to version 2.4.67, which fixes the issue.
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Analysis
by VulDB Data Team • 07/02/2026
The Apache HTTP Server version 2.4.66 contains a critical double free vulnerability within its HTTP/2 protocol implementation that could potentially lead to remote code execution. This vulnerability arises from improper memory management during the processing of HTTP/2 frames, specifically when handling certain malformed or crafted requests. The flaw manifests as a memory corruption issue that occurs when the server attempts to free the same memory block twice during the handling of HTTP/2 connections. This type of vulnerability falls under the common weakness enumeration CWE-415 which categorizes improper free operations and memory management errors that can result in arbitrary code execution when exploited by remote attackers. The vulnerability is particularly dangerous because HTTP/2 is increasingly adopted across modern web deployments, making the attack surface broader than traditional HTTP/1.1 implementations.
The technical exploitation of this vulnerability requires an attacker to send specially crafted HTTP/2 frames to the target server, triggering the double free condition in the memory allocator. When the server processes these malformed frames, it executes a sequence of operations that results in the same memory chunk being deallocated twice, causing heap corruption that can be leveraged for code execution. The attack vector operates through the HTTP/2 protocol layer where the server's handling of stream management and frame processing contains a flaw in the cleanup routines for connection resources. This vulnerability is classified under the attack technique T1211 in the MITRE ATT&CK framework as it involves exploitation of memory corruption vulnerabilities to achieve remote code execution. The impact is severe because the double free condition can be triggered through normal HTTP/2 request processing without requiring authentication or special privileges from the attacker.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it represents a potential path to full system compromise when successfully exploited. Organizations running Apache HTTP Server 2.4.66 with HTTP/2 enabled are at risk of unauthorized remote code execution, which could allow attackers to gain complete control over affected systems. The vulnerability affects all configurations that utilize HTTP/2 protocol handling, including those with SSL/TLS termination, reverse proxy setups, and load balancing configurations that rely on HTTP/2 for performance optimization. Security teams must consider the widespread adoption of HTTP/2 in enterprise environments when assessing the potential impact, as many organizations have migrated to HTTP/2 to improve performance and reduce latency in their web applications.
Immediate mitigation strategies include upgrading to Apache HTTP Server version 2.4.67, which contains the necessary patches to address the double free condition in the HTTP/2 implementation. Organizations unable to perform immediate upgrades should consider disabling HTTP/2 protocol support on affected servers until the patch can be deployed, though this may impact application performance and user experience. Network-level mitigations such as implementing web application firewalls or intrusion detection systems that can detect and block suspicious HTTP/2 traffic patterns may provide temporary protection, though these solutions are not foolproof against sophisticated attacks. Security monitoring should focus on detecting unusual memory allocation patterns or heap corruption indicators in server logs, particularly during HTTP/2 request processing. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date software components, as HTTP/2 implementations require careful attention to memory management practices to prevent such fundamental security flaws from being exploited in production environments.