Excessive CPU Usage Vulnerability in nginx - CVE-2018-16844

nginx Updated 02 Oct 2025

Summary

07/11/2018

Disclosed on

N/A

Severity

Yes i

Fix available

High

Severity

7.5

CVSS Score

ALPINE-CVE-2018-16844: nginx before versions 1.15.6 and 1.14.1 has a vulnerability in the implementation of HTTP/2 that can allow for excessive CPU usage. Affects nginx versions < 1.14.1-r0. Fixed in 1.14.1-r0. How to fix ↓

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Background

nginx is a high-performance web server and reverse proxy server known for its stability, rich feature set, and low resource consumption. It is widely used for serving static content, load balancing, and as a reverse proxy for various applications. However, certain configurations can expose nginx to vulnerabilities, such as CVE-2018-16844, which affects its HTTP/2 implementation.

Vulnerability Detail

The vulnerability identified as CVE-2018-16844 exists in nginx versions prior to 1.15.6 and 1.14.1. It arises from a flaw in the HTTP/2 implementation, which can lead to excessive CPU usage when the 'http2' option is enabled in the 'listen' directive of the configuration file. This can result in denial of service, affecting the availability of the web service and potentially leading to resource exhaustion on the server.

How To Fix

Minimum fixed version

1.14.1-r0

This is the first release that contains the fix.

sudo apk add --upgrade nginx

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Workaround

If immediate patching is not possible, consider disabling the HTTP/2 feature in your nginx configuration by removing or commenting out the 'http2' option in the 'listen' directive. For example: 'listen 80; # http2'. This will mitigate the risk until the package can be updated.

Conclusion

CVE-2018-16844 is a significant vulnerability affecting nginx that can lead to excessive CPU usage. It is crucial to update to the patched version or disable the HTTP/2 feature to mitigate the risk. Regular monitoring for vulnerabilities using tools like Vulert can help maintain the security of your applications.

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