{"id":"GHSA-fph4-wmhf-6fwf","summary":"fast-uri vulnerable to server-side request forgery via repeated hostname percent-decoding","details":"### Impact\n\n`fast-uri` decodes a hostname's percent escapes twice in a single `normalize()` or `resolve()` call: once during parsing and again during authority recomposition. A nested percent-encoded host therefore survives the first decode and is turned into a live destination by the second, so `normalize('http://%256c%256f%2563%2561%256c%2568%256f%2573%2574/')` returns `http://localhost/`. Applications that normalize or resolve an untrusted URI before an SSRF check, redirect validation, or host allowlist can be steered to a different destination, including internal addresses such as loopback or a cloud metadata endpoint, than the encoded input appeared to contain. This is an incomplete-fix variant of CVE-2026-6322, whose encoded-authority-delimiter fix introduced the second decode.\n\n### Patches\n\nFixed in `fast-uri` 2.4.5, 3.1.6, and 4.1.3.\n\n### Workarounds\n\nReject untrusted URIs whose host component contains an encoded percent sign (`%25`) before passing them to `normalize()` or `resolve()`.","aliases":["CVE-2026-75899"],"modified":"2026-09-10T03:50:54.420840001Z","published":"2026-09-02T15:42:39Z","database_specific":{"nvd_published_at":"2026-08-24T10:16:39Z","cwe_ids":["CWE-174","CWE-918"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-09-02T15:42:39Z"},"references":[{"type":"WEB","url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-fph4-wmhf-6fwf"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-75899"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/2642290672e7211c990aaed3749c2ce667d0af4f"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/8c15dbe94ec50bb8e595791ebb42c35cef0fd304"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/commit/ae92a4c5d8c4b6c9e447f048d5fcbde7eebd5514"},{"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/v2.4.5"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v3.1.6"},{"type":"WEB","url":"https://github.com/fastify/fast-uri/releases/tag/v4.1.3"}],"affected":[{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"2.4.1"},{"fixed":"2.4.5"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-fph4-wmhf-6fwf/GHSA-fph4-wmhf-6fwf.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"3.1.2"},{"fixed":"3.1.6"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-fph4-wmhf-6fwf/GHSA-fph4-wmhf-6fwf.json"}},{"package":{"name":"fast-uri","ecosystem":"npm","purl":"pkg:npm/fast-uri"},"ranges":[{"type":"SEMVER","events":[{"introduced":"4.0.0"},{"fixed":"4.1.3"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/09/GHSA-fph4-wmhf-6fwf/GHSA-fph4-wmhf-6fwf.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"}]}