A serious flaw in Apache HTTP Server could allow attackers to run malicious code on vulnerable systems.
Quick Summary – TLDR:
- A high severity flaw tracked as CVE-2026-23918 affects Apache HTTP Server version 2.4.66.
- The bug allows Remote Code Execution through HTTP 2 handling issues.
- Apache released version 2.4.67 on May 4, 2026 with a full fix.
- Several additional vulnerabilities were also patched in the same update.
What Happened?
The Apache Software Foundation has released a critical security update to fix multiple vulnerabilities in Apache HTTP Server, including a high risk flaw that could enable Remote Code Execution. The issue mainly affects version 2.4.66 and requires immediate action from system administrators.
🚨 Apache HTTP Server | CVE-2026-23918 Critical HTTP/2 vulnerability – double free leading to possible RCE. Affects Apache 2.4.66 and earlier.If you’re running Apache:
— Upwind Security MDR (@UpwindMDR) May 4, 2026
• Upgrade to 2.4.67 immediately
• Disable HTTP/2 if not needed
• Monitor for suspicious resets/traffic🔗…
A Dangerous Memory Flaw at the Core
At the center of this security alert is CVE-2026-23918, a high severity vulnerability with a CVSS score of 8.8. The flaw is classified as a double free memory corruption issue, a type of bug that occurs when the server mistakenly frees the same memory block twice.
This issue appears in the way Apache handles HTTP/2 protocol requests. When a specially crafted early reset command is sent, the server mismanages memory and enters an unstable state.
This instability creates two major risks:
- Denial of Service, where the server crashes and goes offline.
- Remote Code Execution, where attackers can run their own commands on the server.
The second scenario is far more dangerous. It can allow attackers to take control of systems, access sensitive data, or deploy malware and ransomware.
Who Discovered the Issue?
The vulnerability was discovered by Bartlomiej Dmitruk from striga.ai and Stanislaw Strzalkowski from isec.pl. They reported the issue privately on December 10, 2025. A fix was developed quickly the next day, but the official patch was only released publicly on May 4, 2026.
More Vulnerabilities Fixed in Same Update
Alongside CVE-2026-23918, the Apache update also addresses four additional vulnerabilities:
- CVE-2026-24072
A moderate severity flaw in mod_rewrite that allows local users to read sensitive files and potentially escalate privileges - CVE-2026-28780
A heap buffer overflow in mod_proxy_ajp that could allow limited memory corruption through malicious AJP servers - CVE-2026-29168
A resource exhaustion issue in mod_md that can overload server resources using oversized responses - CVE-2026-29169
A null pointer issue in mod_dav_lock that can crash the server with a crafted request
While these additional bugs are rated lower in severity, they still contribute to overall risk, especially in complex environments.
Why This Matters?
Apache HTTP Server is one of the most widely used web servers in the world. Its massive global footprint means even a single critical flaw can impact millions of websites and enterprise systems.
The combination of widespread use and Remote Code Execution capability makes this vulnerability particularly serious. Attackers often target web servers as entry points into larger networks.
What Organizations Should Do Now?
Administrators are strongly advised to act immediately:
- Upgrade to Apache HTTP Server 2.4.67 to apply all fixes.
- Disable HTTP/2 temporarily if upgrading is not possible right away.
- Monitor server logs for unusual HTTP/2 activity or crashes.
- Review access controls and configurations to reduce exposure.
- Remove unused modules like mod_dav_lock if not required.
Taking these steps can significantly reduce the risk of exploitation.
SQ Magazine Takeaway
I see this as another reminder that even the most trusted infrastructure tools are not immune to serious flaws. What stands out here is how a single memory issue can open the door to full system compromise. If you are running Apache and delaying updates, you are basically giving attackers a head start. Staying updated is not optional anymore, it is critical.
