{"id":"CVE-2026-84394","aliases":["GHSA-58mr-gqgx-xq4g"],"title":"fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority","summary":"fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority","severity":"high","cvss":7.5,"cwe":["CWE-436"],"vendor":"fast-uri","product":"fast-uri","ecosystem":"npm","affected":["fast-uri = 2.4.5","fast-uri = 3.1.6","fast-uri = 4.1.3"],"patched":["fast-uri 2.4.6","fast-uri 3.1.7","fast-uri 4.1.4"],"published":"2026-09-28","updated":"2026-09-28","sourceUpdated":"2026-09-28T21:23:36Z","source":"GHSA","sourceUrl":"https://github.com/advisories/GHSA-58mr-gqgx-xq4g","references":[{"url":"https://github.com/fastify/fast-uri/security/advisories/GHSA-58mr-gqgx-xq4g"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-84394"},{"url":"https://github.com/fastify/fast-uri/pull/214"},{"url":"https://github.com/fastify/fast-uri/commit/e00815236bc94107e44ef1b2f5318a06bac225c0"},{"url":"https://cna.openjsf.org/security-advisories.html"},{"url":"https://github.com/fastify/fast-uri/releases/tag/v2.4.6"},{"url":"https://github.com/fastify/fast-uri/releases/tag/v3.1.7"},{"url":"https://github.com/fastify/fast-uri/releases/tag/v4.1.4"},{"url":"https://github.com/advisories/GHSA-58mr-gqgx-xq4g"}],"tags":["ghsa","npm"],"ingestedAt":"2026-09-28T22:22:13.613Z","slug":"CVE-2026-84394","body":"## Overview\n\n### Impact\n\n`fast-uri` accepts a host that contains an unbalanced or misplaced authority bracket (`[` or `]`) without reporting an error. A host that starts with `[` but does not end with `]`, such as `[@127.0.0.1`, is neither validated as an IP literal nor canonicalized as a domain name, so `parse()` returns it as the host with `error` undefined, while Node's `URL` (and `http.get`, `axios`, `got`, and other clients built on it) resolve the same string to `127.0.0.1`. An application that reads `parse().host` to make a host decision (an SSRF denylist, a redirect allowlist, or proxy routing) and then passes the original URL to an HTTP client evaluates its policy against a string that is not the host the request reaches. The same host is carried through `normalize()`, `equal()`, and `resolve()`.\n\n### Patches\n\nThis vulnerability has been patched in fast-uri `4.1.4`, `3.1.7`, and `2.4.6`. `parse()` now reports `URI host is malformed.` for any host that contains a bracket but is not a valid `[IPv6]` literal. All users should upgrade.\n\n### Workarounds\n\nIf upgrading is not immediately possible, reject any URL whose host contains a `[` or `]` that is not a well-formed IPv6 literal before making a host decision. Clients that fail closed on credential-bearing URLs, such as Node's global `fetch()`, are not affected by the reported vector.\n\n## Affected packages\n\n- `fast-uri = 2.4.5`\n- `fast-uri = 3.1.6`\n- `fast-uri = 4.1.3`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `fast-uri 2.4.6`\n- `fast-uri 3.1.7`\n- `fast-uri 4.1.4`","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}