{"id":"CVE-2026-86472","aliases":["GHSA-hrr3-gc8f-f4qj"],"url":"https://o3.security/vulnerability/CVE-2026-86472","summary":"fast-uri vulnerable to inconsistent host case normalization via percent-encoded octets","details":"### Impact\n\n`fast-uri` folds the host to lowercase before it percent-decodes the host, so a percent-encoded uppercase unreserved octet such as `%41` decodes to a literal `A` that is never folded. For a scheme-relative reference (`//host`) there is no scheme, so the host canonicalization that repairs this on a scheme-bearing URL does not run. As a result `parse`, `normalize`, and `equal` disagree on the same host: `parse(\"//%41.com\").host` returns `\"A.com\"` while `parse(\"//a.com\").host` and `parse(\"//A.com\").host` return `\"a.com\"`, and `equal(\"//%41.com\", \"//a.com\")` is `false` even though `equal(\"//A.com\", \"//a.com\")` is `true`. An application that makes a case-sensitive host decision on `fast-uri` output for a scheme-relative reference, for example a host allowlist or denylist that compares `parse(url).host` or uses `fast-uri.equal`, can be steered past the check with a percent-encoded uppercase octet. Because a hostname is case-insensitive in DNS and HTTP routing, the evading spelling reaches the same host the check meant to gate, so the effect is check evasion rather than reaching a different registrable host.\n\n### Patches\n\nUpgrade to `fast-uri` 4.1.5, 3.1.8, or 2.4.7.\n\n### Workarounds\n\nCompare hosts case-insensitively (lowercase the parsed host before any allowlist or denylist decision), or avoid making case-sensitive host decisions on scheme-relative input until upgrading.","published":"2026-09-15T10:29:50.594Z","modified":"2026-10-21T03:00:33.457678534Z","cvss":{"score":4.8,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"fast-uri","fixedVersion":"2.4.7"},{"ecosystem":"npm","name":"fast-uri","fixedVersion":"3.1.8"},{"ecosystem":"npm","name":"fast-uri","fixedVersion":"4.1.5"}],"fix":{"url":"https://github.com/fastify/fast-uri/commit/5dabb86732aa2a7655e258719970e61e12b6b4d1","label":"fastify/fast-uri@5dabb86"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86472.json"},{"type":"ADVISORY","url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-hrr3-gc8f-f4qj"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-86472"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/5dabb86732aa2a7655e258719970e61e12b6b4d1"},{"type":"PACKAGE","url":"https://github.com/fastify/fast-uri"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v2.4.7"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v3.1.8"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v4.1.5"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T03:00:33.457678534Z"}}