CVE-2026-61629

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

Published Sep 21, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-jr34-h97m-9hpx nginx ignition has ParseAcceptLanguage `_` separator bypass that enables ~75x CPU amplification via Accept-Language header in i18nMiddleware
History
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Lucasdillmann
Lucasdillmann nginx-ignition
Vendors & Products Lucasdillmann
Lucasdillmann nginx-ignition
Type Values Removed Values Added
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.
Title nginx ignition has ParseAcceptLanguage `_` separator bypass that enables ~75x CPU amplification via Accept-Language header in i18nMiddleware
Weaknesses CWE-770
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Sep 24, 2026, 10:11 PM
Reserved
Jul 10, 2026, 5:38 PM
Status
Awaiting Analysis
Published
Sep 21, 2026, 3:17 PM
Modified
Sep 24, 2026, 11:17 PM