Memory Consumption Vulnerability in nginx: CVE-2018-16843

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-2018-16843: nginx before versions 1.15.6 and 1.14.1 has a vulnerability in the implementation of HTTP/2 that can allow for excessive memory consumption. 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. The vulnerability in question affects nginx versions prior to 1.15.6 and 1.14.1, specifically when compiled with the ngx_http_v2_module, which is not enabled by default. This vulnerability can lead to excessive memory consumption under certain configurations.

Vulnerability Detail

The vulnerability identified as CVE-2018-16843 arises from a flaw in the HTTP/2 implementation of nginx. When the 'http2' option is enabled in the 'listen' directive of the configuration file, it can lead to excessive memory usage, potentially causing denial of service. This issue affects users who have configured nginx to use HTTP/2, particularly those who have not updated to the patched versions. The CVSS score for this vulnerability is 7.5, indicating a high severity level.

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 you cannot update nginx immediately, consider disabling the HTTP/2 option in your configuration file. You can do this by removing or commenting out the 'http2' directive in your 'listen' configuration. For example: 'listen 443 ssl; # http2'. This will prevent the vulnerability from being exploited until you can apply the patch.

Conclusion

The CVE-2018-16843 vulnerability in nginx poses a significant risk due to its potential for excessive memory consumption. Users are advised to update to the patched versions or implement workarounds to mitigate the risk until an update can be applied. Regular monitoring for vulnerabilities using tools like Vulert can help maintain the security of your applications.

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