{"id":"GHSA-7p8r-x3mc-p8w7","summary":"fast-uri vulnerable to host confusion via backslash authority introducer","details":"### Impact\n\n`fast-uri` v4.1.1 and earlier require a literal `//` to recognize a URI authority, so a reference that uses `\\\\`, `/\\`, or `\\/` as the authority introducer (in place of `//`, after an optional scheme) is parsed with no authority: the sequence and everything after it fold into the path. Node's native WHATWG `URL` (used by `fetch()`, `undici`, and Node's `http`/`https` clients) instead treats `\\` as interchangeable with `/` for special schemes (`http`, `https`, `ws`, `wss`, `ftp`, `file`), so the two parsers extract different hosts from the same input.\n\nFor example, `fast-uri` resolves `\\\\evil.com/path` against base `https://allowed.com/` to `https://allowed.com/%5C%5Cevil.com/path` (confined to the trusted host), while Node's WHATWG URL resolves the same reference to `https://evil.com/path`.\n\nApplications that use `fast-uri` to enforce host-based policy (allowlists, denylists, loopback/SSRF filtering, redirect validation, outbound proxy routing) before passing the same URL into Node's URL or `fetch()` consumers see a policy/use desync and can be steered to an unintended destination.\n\n### Patches\n\nUpgrade to `fast-uri` v4.1.2, v3.1.5, v2.4.4.\n\n### Workarounds\n\nNone. Upgrade to the patched version.","aliases":["CVE-2026-18446"],"modified":"2026-08-03T19:30:08.078883358Z","published":"2026-08-03T19:16:43Z","database_specific":{"cwe_ids":["CWE-436"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-08-03T19:16:43Z","nvd_published_at":"2026-07-31T15:16:27Z"},"references":[{"type":"WEB","url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-7p8r-x3mc-p8w7"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-18446"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/f3c6c905f47831007490f466c5945012e905cc52"},{"type":"WEB","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"PACKAGE","url":"https://github.com/fastify/fast-uri"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v4.1.2"}],"affected":[{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.4.4"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-7p8r-x3mc-p8w7/GHSA-7p8r-x3mc-p8w7.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"3.0.0"},{"fixed":"3.1.5"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-7p8r-x3mc-p8w7/GHSA-7p8r-x3mc-p8w7.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.0"},{"fixed":"4.1.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-7p8r-x3mc-p8w7/GHSA-7p8r-x3mc-p8w7.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"}]}