CVE-2026-84394: Fast uri Fast-uri Vulnerable To Host Confusion Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-58mr-gqgx-xq4g",
  "modified" : "2026-09-28T21:23:36Z",
  "published" : "2026-09-28T21:23:35Z",
  "aliases" : [ "CVE-2026-84394" ],
  "summary" : "fast-uri vulnerable to host confusion via an unclosed bracket in the URI authority",
  "details" : "### 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fast-uri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.4.5"
      }, {
        "fixed" : "2.4.6"
      } ]
    } ],
    "versions" : [ "2.4.5" ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fast-uri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.1.6"
      }, {
        "fixed" : "3.1.7"
      } ]
    } ],
    "versions" : [ "3.1.6" ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fast-uri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.1.3"
      }, {
        "fixed" : "4.1.4"
      } ]
    } ],
    "versions" : [ "4.1.3" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/security/advisories/GHSA-58mr-gqgx-xq4g"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-84394"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/pull/214"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/commit/e00815236bc94107e44ef1b2f5318a06bac225c0"
  }, {
    "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/v2.4.6"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/releases/tag/v3.1.7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/releases/tag/v4.1.4"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-436" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-28T21:23:35Z",
    "nvd_published_at" : "2026-09-03T05:16:38Z"
  }
}