Nginx Denial of Service Vulnerability and Regression Issues
Severity: High (Score: 70.5)
Sources: Linuxsecurity, launchpad.net, Ubuntu
Published: · Updated:
Keywords: ubuntu, nginx, issue, made, consume, excessive, denial
Severity indicators: issue, rce
Summary
A vulnerability in nginx was discovered that allows remote attackers to cause excessive resource consumption through specially crafted HTTP/2 cookie headers, leading to denial of service (CVE-2026-49975). The initial fix for this vulnerability introduced a regression causing nginx to crash when used with external modules. This regression has prompted a reversion of the fix pending further investigation. Affected systems include multiple Ubuntu LTS versions, specifically 26.04, 25.10, 24.04, and 22.04. Users are advised to update their systems to mitigate the risk. The vulnerability was published on June 8, 2026, with a proof of concept available since June 4, 2026. The situation is ongoing, with further updates expected. Key Points: • Nginx vulnerability allows denial of service via crafted HTTP/2 cookie headers. • Regression from a fix caused nginx to crash when using external modules. • Affected Ubuntu versions include 26.04 LTS and earlier releases.
Detailed Analysis
**Impact** Ubuntu users across multiple LTS and interim releases (22.04, 24.04, 25.10, 26.04) are affected by this vulnerability in nginx, a widely deployed web and proxy server. The flaw allows remote attackers to cause nginx to consume excessive resources, leading to denial of service conditions that can disrupt business operations relying on web services. No specific data theft or integrity compromise is reported, but service availability is impacted. **Technical Details** The vulnerability (CVE-2026-49975) arises from incorrect handling of certain cookie headers in nginx's HTTP/2 implementation. Exploitation involves sending specially crafted network traffic to trigger excessive resource consumption. The initial patch introduced a regression causing crashes with external modules, leading to a temporary reversion of the fix pending further investigation. No malware or additional tools are mentioned, and no IOCs are provided. **Recommended Response** Apply the latest nginx package updates provided by Ubuntu for your specific release to remediate the vulnerability, noting that the initial fix was reverted due to regression issues. Monitor nginx service stability and logs for crashes or unusual resource usage. Maintain updated system packages and track Ubuntu security advisories for a revised patch addressing both the vulnerability and regression.
Source articles (5)
- USN-8398-1: nginx vulnerability — Ubuntu · 2026-06-08
nginx could be made to consume excessive resources if it received specially crafted network traffic. It was discovered that nginx incorrectly handled certain cookie headers in the HTTP/2 implementatio… - 1.18.0-6ubuntu14.13 — launchpad.net · 2026-06-08
The nginx_http_auth_pam module enables authentication using PAM. . The module uses PAM as a backend for simple http authentication. It also allows setting the pam service name to allow more fine grain… - Ubuntu 26.04 LTS nginx Denial of Service Resource Issue Vuln USN-8398 — Linuxsecurity · 2026-06-08
A security issue affects these releases of Ubuntu and its derivatives: - Ubuntu 26.04 LTS - Ubuntu 25.10 - Ubuntu 24.04 LTS - Ubuntu 22.04 LTS Summary: nginx could be made to consume excessive resourc… - USN-8398-2: nginx regression — Ubuntu · 2026-06-09
USN-8398-1 fixed a vulnerability in nginx. The update introduced a regression causing nginx to crash when being used with external modules. This update reverts the fix for CVE-2026-49975 pending furth… - 1.18.0-6ubuntu14.14 — launchpad.net · 2026-06-09
The nginx_http_auth_pam module enables authentication using PAM. . The module uses PAM as a backend for simple http authentication. It also allows setting the pam service name to allow more fine grain…
Timeline
- 2026-06-04 — First public PoC for CVE-2026-49975: A proof of concept was made available for a vulnerability in nginx affecting resource consumption.
- 2026-06-08 — CVE-2026-49975 published: The vulnerability was officially published, detailing how nginx mishandled HTTP/2 cookie headers.
- 2026-06-08 — Regression issue identified: The fix for CVE-2026-49975 caused nginx to crash when used with external modules, prompting a reversion of the fix.
- Recent — Users advised to update systems: Affected users are encouraged to update their nginx installations to mitigate the denial of service risk.
CVEs
Related entities
- DDoS (Attack Type)
- Denial of Service (Attack Type)
- Ubuntu (Company)
- Apache (Platform)
- Nginx (Tool)