Overview
NSFOCUS CERT recently noted that Apache had released a security advisory announcing a fix for a remote code execution vulnerability (CVE-2026-119618) in Apache HTTP Server. Due to improper synchronization when accessing shared resources in the assign_headers() function of Apache HTTP Server’s mod_http2 module, an unauthenticated attacker could trigger a race condition by sending concurrent HTTP/2 requests, resulting in heap memory corruption. Under certain conditions, the attacker could execute arbitrary code with the privileges of the web server. The vulnerability has a CVSS score of 9.8. Details of the vulnerability and a proof of concept (PoC) demonstrating a denial-of-service (DoS) condition are now publicly available. Affected users are advised to take mitigation measures as soon as possible.
Apache HTTP Server (httpd) is a widely deployed open-source web server. Its mod_http2 module provides support for the HTTP/2 protocol, significantly improving data transfer performance and concurrency in modern web applications.
Reference: https://www.mail-archive.com/announce@apache.org/msg12665.html
Scope of Impact
Affected Versions
- 2.4.55 <= Apache HTTP Server <= 2.4.70
- 2.0.8 <= mod_h2 <= 2.0.42
Note: Apache HTTP Server is affected only if HTTP/2 (h2 or h2c) is enabled.
Unaffected Versions
- Apache HTTP Server >= 2.4.71
- mod_h2 > 2.0.42
Detection
Manual Detection
Users can determine whether their deployment is at risk by checking the Apache HTTP Server version and whether HTTP/2 is enabled:
Check the current Apache HTTP Server version:
httpd -v
# On some Linux distributions (e.g., Debian/Ubuntu):
apache2 -v
Check whether the http2_module module is loaded:
httpd -M | grep http2
# Or:
apache2ctl -M | grep http2
Check whether HTTP/2 (h2 or h2c) is enabled via the Protocols directive in the configuration files:
grep -rn “Protocols” /etc/httpd/ /etc/apache2/ 2>/dev/null
If the installed version falls within the affected range and HTTP/2 (h2 or h2c) is enabled on the server, the deployment may be vulnerable.
Mitigation
Official Security Update
Apache has released an updated version that addresses this vulnerability. Affected users are advised to upgrade as soon as possible.
Download link: https://httpd.apache.org/download.cgi
Additional Mitigation Measures
Where operational requirements permit, users can temporarily mitigate the vulnerability by disabling HTTP/2:
Modify the configuration files:
Modify the main Apache configuration file (e.g., httpd.conf or apache2.conf) or the relevant virtual host configuration file to enable only HTTP/1.1:
Protocols http/1.1
Verify the configuration and restart the service:
systemctl restart httpd
# On some Linux distributions (e.g., Debian/Ubuntu):
systemctl restart apache2
Statement
This advisory is only used to describe a potential risk. NSFOCUS does not provide any commitment or promise on this advisory. NSFOCUS and the author will not bear any liability for any direct and/or indirect consequences and losses caused by transmitting and/or using this advisory. NSFOCUS reserves all the rights to modify and interpret this advisory. Please include this statement paragraph when reproducing or transferring this advisory. Do not modify this advisory, add/delete any information to/from it, or use this advisory for commercial purposes without permission from NSFOCUS.
About NSFOCUS
NSFOCUS, a pioneering leader in cybersecurity, is dedicated to safeguarding telecommunications, Internet service providers, hosting providers, and enterprises from sophisticated cyberattacks.
Founded in 2000, NSFOCUS operates globally with over 3000 employees at two headquarters in Beijing, China, and Santa Clara, CA, USA, and over 50 offices worldwide. It has a proven track record of protecting over 25% of the Fortune Global 500 companies, including four of the five largest banks and six of the world’s top ten telecommunications companies.
Leveraging technical prowess and innovation, NSFOCUS delivers a comprehensive suite of security solutions, including the Intelligent Security Operations Platform (ISOP) for modern SOC, DDoS Protection, Continuous Threat Exposure Management (CTEM) Service and Web Application and API Protection (WAAP). All the solutions and services are augmented by the Security Large Language Model (SecLLM), ML, patented algorithms and other cutting-edge research achievements developed by NSFOCUS.
