{"id":"GHSA-v2hh-gcrm-f6hx","summary":"fast-uri vulnerable to host confusion via literal backslash authority delimiter","details":"### Impact\n\n`fast-uri` v4.1.0 and earlier do not treat a literal backslash (U+005C) as an authority delimiter. Node's native WHATWG `URL` (used by `fetch()`, `undici`, and Node's `http`/`https` clients) normalizes `\\` to `/` for special schemes (`http`, `https`, `ws`, `wss`, `ftp`, `file`), so the two parsers extract different hosts from the same input string.\n\nFor example, `http://evil.com\\@allowed.com` is treated by `fast-uri` as host `allowed.com` with userinfo `evil.com\\`, while Node's WHATWG URL parser and `fetch()` see host `evil.com` with path `/@allowed.com`.\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, including cloud metadata endpoints, loopback, or internal hosts.\n\n### Patches\n\nUpgrade to `fast-uri` v4.1.1, v3.1.4, or v2.4.3.\n\n### Workarounds\n\nNone. Upgrade to the patched version.","aliases":["CVE-2026-16221"],"modified":"2026-09-10T03:51:12.051886648Z","published":"2026-07-21T22:08:28Z","database_specific":{"nvd_published_at":"2026-07-19T15:16:49Z","cwe_ids":["CWE-436"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-07-21T22:08:28Z"},"references":[{"type":"WEB","url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-v2hh-gcrm-f6hx"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-16221"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/0542a216860fd70c062a4730e620576f62ded057"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/2d50fbabc80e4d0884fe0f6a98fe118ce6faa353"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/9438266d6a7ded688c8bc7c4ba506da17f44a17b"},{"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/v2.4.3"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v3.1.4"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v4.1.1"}],"affected":[{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.3.1"},{"fixed":"2.4.3"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 2.4.2","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-v2hh-gcrm-f6hx/GHSA-v2hh-gcrm-f6hx.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"3.0.0"},{"fixed":"3.1.4"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 3.1.3","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-v2hh-gcrm-f6hx/GHSA-v2hh-gcrm-f6hx.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.0"},{"fixed":"4.1.1"}]}],"database_specific":{"last_known_affected_version_range":"\u003c= 4.1.0","source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/07/GHSA-v2hh-gcrm-f6hx/GHSA-v2hh-gcrm-f6hx.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"}]}