Summary

CVE-2026-23918 is a high-severity security vulnerability affecting the Apache HTTP Server, specifically version 2.4.66. The flaw involves a double-free error within the HTTP/2 protocol handling, carrying CVSS score of 8.8. Exploitation of this vulnerability can lead to Denial of Service (DoS) and potentially Remote Code Execution (RCE). Security researchers Bartlomiej Dmitruk and Stanislaw Strzalkowski are credited with discovering and reporting the issue. The Apache Software Foundation has released security updates to address this vulnerability. Public proof-of-concept exploit code is currently available for the DoS path with work underway on the RCE path; the researchers were able to privately achieve RCE and while they did not provide working code, they did provide a relatively detailed outline of how their exploit works. The bug's in-the-wild exploitation status is currently unknown.

Affected Systems and/or Applications

Apache HTTP Server version 2.4.66. Fixed in 2.4.67.

Technical Details

The vulnerability arises from a double-free condition in the HTTP/2 module of the Apache HTTP Server. A double-free error occurs when memory is deallocated more than once, leading to heap corruption. Attackers can exploit this memory corruption to crash the server, causing a DoS, or potentially manipulate memory to execute arbitrary code remotely. The issue specifically impacts the handling of HTTP/2 requests. - DoS is trivial and works on any default Apache deployment with mod_http2 and a multi-threaded MPM (multi-processing module). - RCE is more complex. Successful exploitation requires an APR (Apache Portable Runtime) with the mmap allocator; this is the default on Debian-derived systems as well as the official httpd Docker image.

Mitigation

• Apply Patches: Immediately update Apache HTTP Server to the latest patched version provided by the Apache Software Foundation (2.4.67 at time of writing.)
• Disable HTTP/2 (Temporary Workaround): If immediate patching is not feasible, administrators can disable HTTP/2 support in the Apache configuration to mitigate the risk, though this will revert client connections to HTTP/1.1 and may impact performance.

What the Cyber Fusion Center is Doing

The Cyber Fusion Center (CFC) is monitoring the situation and will issue advisory updates as needed.

References

• Apache HTTP Server 2.4 vulnerabilities - The Apache HTTP Server Project
• CVE-2026-23918 - CVE Record
• Critical Apache HTTP/2 Flaw (CVE-2026-23918) Enables DoS and RCE

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