{"id":"CVE-2026-30827","aliases":["GHSA-46wh-pxpv-q5gq"],"url":"https://o3.security/vulnerability/CVE-2026-30827","summary":"express-rate-limit: IPv4-mapped IPv6 addresses bypass per-client rate limiting (all IPv4 clients share one bucket on dual-stack servers)","details":"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.","published":"2026-03-07T05:19:08.206Z","modified":"2026-08-07T11:49:52.598673233Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"express-rate-limit","fixedVersion":"8.2.2"},{"ecosystem":"npm","name":"express-rate-limit","fixedVersion":"8.1.1"},{"ecosystem":"npm","name":"express-rate-limit","fixedVersion":"8.0.2"}],"fix":{"url":"https://github.com/express-rate-limit/express-rate-limit/commit/14e53888cdfd1b9798faf5b634c4206409e27fc4","label":"express-rate-limit/express-rate-limit@14e5388"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/30xxx/CVE-2026-30827.json"},{"type":"ADVISORY","url":"https://github.com/express-rate-limit/express-rate-limit/security/advisories/GHSA-46wh-pxpv-q5gq"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-30827"},{"type":"FIX","url":"https://github.com/express-rate-limit/express-rate-limit/commit/14e53888cdfd1b9798faf5b634c4206409e27fc4"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:49:52.598673233Z"}}