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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-61629
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-21 15:17:30 UTC
Updated2026-09-21 15:17:30 UTC
Descriptionnginx 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.

Risk And Classification

Primary CVSS: v3.1 7.5 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS: 0.003580000 probability, percentile 0.296490000 (date 2026-09-22)

Problem Types: CWE-770 | CWE-770 CWE-770: Allocation of Resources Without Limits or Throttling

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.1CNADECLARED7.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Lucasdillmann Nginx-ignition affected >= 2.29.0, < 2.40.1 Not specified

References

ReferenceSourceLinkTags
github.com/lucasdillmann/nginx-ignition/commit/0c988fc1277c7d291725e8373... [email protected] github.com
github.com/lucasdillmann/nginx-ignition/security/advisories/GHSA-jr34-h9... [email protected] github.com
github.com/lucasdillmann/nginx-ignition/commit/cbaf0fc16ed873f7178a2ca9b... [email protected] github.com
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