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

{
  "id": "fb5b65b35ae0cd74a0b9974b0259a0242bfb2451ff3a1b927fabd4b0fba790cc",
  "url": "https://osv.dev/vulnerability/CVE-2026-61629",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "nginx ignition has ParseAcceptLanguage `_` separator bypass that enables ~75x CPU amplification via Accept-Language header in i18nMiddleware",
    "summary": "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.",
    "evidence": "osv:CVE-2026-61629",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-61629",
      "aliases": [
        "CVE-2026-61629",
        "GHSA-jr34-h97m-9hpx",
        "GO-2026-6539"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/lucasdillmann/nginx-ignition",
              "type": "GIT",
              "events": [
                {
                  "introduced": "268a7816033a9df678538c594013af709dbf63be"
                },
                {
                  "fixed": "0c988fc1277c7d291725e8373313f8486fa1b31a"
                },
                {
                  "fixed": "cbaf0fc16ed873f7178a2ca9b0d00a696e44b485"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "2.29.0"
                      },
                      {
                        "fixed": "2.40.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "0c988fc1277c7d291725e8373313f8486fa1b31a"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "cbaf0fc16ed873f7178a2ca9b0d00a696e44b485"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2.40.0",
            "2.39.0",
            "2.38.0",
            "2.37.0",
            "2.36.1",
            "2.36.0",
            "2.35.3",
            "2.35.2",
            "2.35.1",
            "2.35.0",
            "2.34.0",
            "2.33.0",
            "2.32.0",
            "2.31.2",
            "2.31.1",
            "2.31.0",
            "2.30.0",
            "2.29.1",
            "2.29.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-61629.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:38.909675099Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61629.json",
        "https://github.com/lucasdillmann/nginx-ignition/security/advisories/GHSA-jr34-h97m-9hpx",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-61629",
        "https://github.com/lucasdillmann/nginx-ignition/commit/0c988fc1277c7d291725e8373313f8486fa1b31a",
        "https://github.com/lucasdillmann/nginx-ignition/commit/cbaf0fc16ed873f7178a2ca9b0d00a696e44b485"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/61xxx/CVE-2026-61629.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-61629",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 506199,
  "published_at": "2026-09-21T14:22:34.126+00:00"
}