express-rate-limit: IPv4-mapped IPv6 addresses bypass per-client rate limiting (all IPv4 clients share one bucket on dual-stack servers)

{
  "id": "c45db876c8d52308843f7a68451b14ebe2fc56a72847da7abb1997f87501b4e5",
  "url": "https://osv.dev/vulnerability/CVE-2026-30827",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "express-rate-limit: IPv4-mapped IPv6 addresses bypass per-client rate limiting (all IPv4 clients share one bucket on dual-stack servers)",
    "summary": "express-rate-limit is a basic rate-limiting middleware for Express. In versions starting from 8.0.0 and prior to versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0, the default keyGenerator in express-rate-limit applies IPv6 subnet masking (/56 by default) to all addresses that net.isIPv6() returns true for. This includes IPv4-mapped IPv6 addresses (::ffff:x.x.x.x), which Node.js returns as request.ip on dual-stack servers. Because the first 80 bits of all IPv4-mapped addresses are zero, a /56 (or any /32 to /80) subnet mask produces the same network key (::/56) for every IPv4 client. This collapses all IPv4 traffic into a single rate-limit bucket: one client exhausting the limit causes HTTP 429 for all other IPv4 clients. This issue has been patched in versions 8.0.2, 8.1.1, 8.2.2, and 8.3.0.",
    "evidence": "osv:CVE-2026-30827",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-30827",
      "aliases": [
        "CVE-2026-30827",
        "GHSA-46wh-pxpv-q5gq"
      ],
      "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/express-rate-limit/express-rate-limit",
              "type": "GIT",
              "events": [
                {
                  "introduced": "c299d5c89f9a75e52bfc28b81c22df0f059520e8"
                },
                {
                  "fixed": "54a685fbc4e8f88839349677e54e52380ad374c8"
                },
                {
                  "introduced": "37347330ecb5e0f6e34a278fa77502b3572f57f7"
                },
                {
                  "fixed": "a009ad6488448515b219eb9f4203c725eb328c8e"
                },
                {
                  "introduced": "60619359e1a479cceaf5893c0eb4ec68a99d5347"
                },
                {
                  "fixed": "14e53888cdfd1b9798faf5b634c4206409e27fc4"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:express-rate-limit_project:express-rate-limit:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "8.0.0"
                      },
                      {
                        "fixed": "8.0.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:express-rate-limit_project:express-rate-limit:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "8.2.0"
                      },
                      {
                        "fixed": "8.2.2"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "cpe": "cpe:2.3:a:express-rate-limit_project:express-rate-limit:8.1.0:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "8.1.0"
                      },
                      {
                        "last_affected": "8.1.0"
                      }
                    ],
                    "source": "CPE_STRING"
                  },
                  {
                    "range": [
                      {
                        "fixed": "14e53888cdfd1b9798faf5b634c4206409e27fc4"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "8.1.0",
            "v8.0.1",
            "v8.2.1",
            "v8.2.0",
            "v8.0.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-30827.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:24.072871612Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/30xxx/CVE-2026-30827.json",
        "https://github.com/express-rate-limit/express-rate-limit/security/advisories/GHSA-46wh-pxpv-q5gq",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-30827",
        "https://github.com/express-rate-limit/express-rate-limit/commit/14e53888cdfd1b9798faf5b634c4206409e27fc4"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-770"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/30xxx/CVE-2026-30827.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-30827",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 490398,
  "published_at": "2026-03-07T05:19:08.206+00:00"
}