Moderate Security Update for mod_http2: Addressing HTTP/2 DoS Vulnerability
Summary
ALSA-2026:22551: Moderate: mod_http2 security update. Affects mod_http2 versions < 2.0.26-6.el9_8. Fixed in 2.0.26-6.el9_8. How to fix ↓
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Background
The mod_h2 module for Apache HTTP Server enables the implementation of the HTTP/2 protocol, enhancing web performance and efficiency. It is built on top of libnghttp2 and is essential for servers running httpd 2.4. However, vulnerabilities in this module can lead to significant security risks, including denial of service (DoS) attacks, which can disrupt service availability.
Vulnerability Detail
The vulnerability identified as CVE-2025-53020 allows for a denial of service (DoS) attack through memory increase. Attackers can exploit this flaw to consume excessive memory resources, potentially leading to server crashes or unresponsiveness. This issue arises from the way the mod_h2 module handles HTTP/2 requests, making it critical for users to address it promptly to maintain server integrity and availability.
How To Fix
Minimum fixed version
2.0.26-6.el9_8
This is the first release that contains the fix.
sudo dnf update mod_http2Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, you may consider disabling the HTTP/2 protocol in your Apache configuration until the update can be applied. This can be done by commenting out or removing the 'Protocols h2 h2c' line in your Apache configuration file, typically located at /etc/httpd/conf/httpd.conf.
Conclusion
The mod_http2 module for Apache HTTP Server is critical for implementing the HTTP/2 protocol, but it is susceptible to a denial of service vulnerability (CVE-2025-53020). Users are urged to update to the patched version to safeguard their servers against potential attacks. Utilizing tools like Vulert can further enhance your security posture by monitoring for vulnerabilities in real-time.
See every vulnerability recorded for mod_http2 →
FAQ
mod_http2 is an Apache HTTP Server module that implements the HTTP/2 protocol, allowing for improved web performance and resource management.
CVE-2025-53020 is the identifier for a vulnerability in mod_http2 that allows for denial of service attacks through excessive memory consumption.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
The vulnerability can lead to service disruptions, server crashes, and unavailability of web services due to excessive memory usage.
Yes, Vulert provides a solution that monitors and alerts for open-source vulnerabilities in your software using just a manifest file like package-lock.json.
Related vulnerabilities
Recent vulnerabilities recorded for mod_http2.
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