CVE-2026-23918 is a CVSS 8.8 double free RCE vulnerability in Apache HTTP Server 2.4.66 that is triggered by an HTTP/2 early reset. A version 2.4.67 patch was released on May 4, 2026 but millions of servers worldwide are still vulnerable. Read this article or learn how to upgrade immediately otherwise attackers could execute arbitrary code on your server.
Roughly 30 percent of the Internet traffic passes through Apache HTTP Server. The web portal of every major bank, the backend of every government website, and the core of thousands of enterprise applications run on Apache. Now imagine if that same server had a silently hidden vulnerability that could give an attacker complete control of the server with just one crafted request.
This is CVE-2026-23918 and this is why the disclosure of this flaw on May 4, 2026 became a global cybersecurity alert. The Apache Software Foundation released version 2.4.67 which patches a dangerous double-free flaw that existed in the HTTP/2 protocol implementation and could enable remote code execution.
All users running version 2.4.66 or older must upgrade immediately. This update is not just a routine security patch. Its an emergency response to a flaw that remained unpatched for five months from December 2025 to May 2026.
The only thing that makes this vulnerability technically disturbing is the memory management failure at the core of this flaw. CVE-2026-23918 is a double free memory corruption issue that specifically exists in the Apache HTTP Server’s HTTP/2 protocol handling. When a specially crafted early reset frame is sent, the server mishandles its memory allocation and tries to free the same memory block twice.
This creates unstable memory behavior that attackers can exploit. In less severe cases this flaw crashes the server and creates a Denial of Service condition but in advanced exploitation scenarios attackers can achieve Remote Code Execution.
Double free is a classic category vulnerability considered one of the most dangerous in low-level programming because once heap memory is corrupted and the attacker has a path that can lead to malicious code execution. This flaw was reported to the Apache team by Bartlomiej Dmitruk of striga.ai and Stanislaw Strzalkowski of isec.pl on December 10, 2025.
The fix was committed the very next day i.e. December 11, but the official patched release, version 2.4.67 was made public on May 4, 2026. This means that within a window of five months, the flaw was technically fixed but there was no deployment.
Along with this CVE Apache has also addressed four more vulnerabilities in the same 2.4.67 update. CVE-2026-24072 is a moderate severity flaw that targets the ap_expr expression evaluation of mod_rewrite and allows local .htaccess authors to read arbitrary files with the privileges of the httpd user.
CVE-2026-28780 is a heap-based buffer overflow in mod_proxy_jp that could write up to 4 attacker controlled bytes from the heap buffer when receiving a crafted message from a malicious AJP server.
CVE-2026-29169 is a NULL pointer dereference in mod_dav_lock that could cause a server crash with a malicious request. CVE-2026-27804 is a timing attack in mod_auth_digest that allows digest authentication bypass by measuring response delays.
These five vulnerabilities together could form a coordinated attack chain where they first achieve RCE with CVE-2026-23918, then read sensitive files with CVE-2026-24072 and complete authentication bypass with CVE-2026-27804.
Patch Released Millions Still Vulnerable
Apache HTTP Server 2.4.67 delivers a critical double free correction in HTTP/2 that prevents remote code execution when clients send early reset frames under heavy load. The update also includes a timing attack patch on digest authentication that prevents attackers from bypassing credentials by measuring response delays to repeated requests.
The release also addresses HTTP response splitting vulnerabilities that occur when multiple modules forward malicious status lines from compromised upstream servers. CVSS score is 8.8 Attack vector is network Attack complexity is low Privileges required are low and no user interaction is needed which meaning a low-privileged user can remotely trigger this flaw without any action from the victim. Technical Impact is total which meaning both confidentiality, integrity, and availability can be compromised
If patching is not immediately possible temporarily disable HTTP/2 support by removing h2 from the Protocols directive or setting Protocols to http/1.1. Monitor server access and error logs for unusual HTTP/2 traffic patterns or unexpected server crashes that may indicate an exploitation attempt.
Remove mod_dav_lock if that module is not in active use as it provides an interim mitigation for CVE-2026-29169. Audit htaccess permissions to limit exposure to CVE-2026-24072 in environments where local user access is concerned. This flaw exposes a fundamental layer of the internet infrastructure. Apache is not just software and it is the foundation on which a large part of the web rests.
When that foundation cracks, everything above is at risk. Upgrading to version 2.4.67 should be your number one priority right now because while you wait hackers are taking control of someone else server.
