Vulnerability · Published Sep 21, 2026 · Assigned by GitHub_M

CVE-2026-61629nginx ignition has ParseAcceptLanguage `_` separator bypass that enables ~75x CPU amplification via Accept-Language header in i18nMiddleware

High 7.5

In plain English

A high-severity resource allocation without limits in nginx-ignition from lucasdillmann. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 37% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.4%top 63.4% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

nginx ignition is a user interface for the nginx web server. In versions 2.29.0 through 2.40.0, the gin i18n middleware in nginx-ignition's API server runs in front of every HTTP request and calls `golang.org/x/text/language.ParseAcceptLanguage` on the raw `Accept-Language` header without imposing any size or shape filter. The underlying parser has quadratic-time behaviour on long lists of malformed language tags. The CVE-2022-32149 guard that golang.org/x/text added in v0.3.8 caps the number of `-` characters in the input at 1000, but it does not cap `_` characters even though the parser's internal scanner aliases `_` to `-` before parsing. A single unauthenticated GET request with an `Accept-Language` header built out of `_` separators burns about 2.4 seconds of server CPU on the host running nginx-ignition; ten concurrent attackers saturate a ten-core box for the duration of the attack while consuming ~10 MiB/s of upstream bandwidth. Version 2.40.1 fixes this issue.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/lucasdillmann/nginx-ignition	0.0.0-20260526022344-0c988fc1277c	GHSA-jr34-h97m-9hpx
Go	github.com/lucasdillmann/nginx-ignition	0.0.0-20260526022344-0c988fc1277c	GO-2026-6539
Ubuntu:22.04:LTS	nginx	no fix listed	UBUNTU-CVE-2026-61629
Ubuntu:24.04:LTS	nginx	no fix listed	UBUNTU-CVE-2026-61629
Ubuntu:26.04:LTS	nginx	no fix listed	UBUNTU-CVE-2026-61629

Affected products (as reported)

Vendor	Product	Versions
lucasdillmann	nginx-ignition	>= 2.29.0, < 2.40.1

Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/lucasdillmann/nginx-ignition/security/advisories/GHSA-jr34-h97m-9hpx x_refsource_CONFIRM
https://github.com/lucasdillmann/nginx-ignition/commit/0c988fc1277c7d291725e8373313f8486fa1b31a x_refsource_MISC
https://github.com/lucasdillmann/nginx-ignition/commit/cbaf0fc16ed873f7178a2ca9b0d00a696e44b485 x_refsource_MISC