CVE-2026-61629 nginx ignition has ParseAcceptLanguage `_` separator bypass that enables ~75x CPU amplification via Accept-Language header in i18nMiddleware
Unauthenticated attackers can cause CPU exhaustion and denial of service in nginx-ignition by sending crafted Accept-Language headers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-61629?
CVE-2026-61629 is a high-severity denial of service vulnerability in lucasdillmann nginx-ignition, published on 21 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-770
Which versions are affected by CVE-2026-61629?
3 open source packages ship an affected version, including github.com/lucasdillmann/nginx-ignition.
| Package | Affected | Fixed in |
|---|---|---|
github.com/lucasdillmann/nginx-ignition Go | From 0.0.0-20260126024607-cbaf0fc16ed8 | 0.0.0-20260526022344-0c988fc1277c |
github.com/lucasdillmann/nginx-ignition Go | From 0.0.0-20260126024607-cbaf0fc16ed8 | 0.0.0-20260526022344-0c988fc1277c |
github.com/lucasdillmann/nginx-ignition Go | From 0.0.0-20260126024607-cbaf0fc16ed8 | 0.0.0-20260526022344-0c988fc1277c |
How do I fix CVE-2026-61629?
Upgrade github.com/lucasdillmann/nginx-ignition to 0.0.0-20260526022344-0c988fc1277c or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-61629 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-61629 exists.
Sources
Also known as GHSA-jr34-h97m-9hpx, GO-2026-6539.