CVE-2026-86472: Fast uri Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hrr3-gc8f-f4qj",
  "modified" : "2026-09-29T23:54:26Z",
  "published" : "2026-09-29T23:54:25Z",
  "aliases" : [ "CVE-2026-86472" ],
  "summary" : "fast-uri vulnerable to inconsistent host case normalization via percent-encoded octets",
  "details" : "### Impact\n\n`fast-uri` folds the host to lowercase before it percent-decodes the host, so a percent-encoded uppercase unreserved octet such as `%41` decodes to a literal `A` that is never folded. For a scheme-relative reference (`//host`) there is no scheme, so the host canonicalization that repairs this on a scheme-bearing URL does not run. As a result `parse`, `normalize`, and `equal` disagree on the same host: `parse(\"//%41.com\").host` returns `\"A.com\"` while `parse(\"//a.com\").host` and `parse(\"//A.com\").host` return `\"a.com\"`, and `equal(\"//%41.com\", \"//a.com\")` is `false` even though `equal(\"//A.com\", \"//a.com\")` is `true`. An application that makes a case-sensitive host decision on `fast-uri` output for a scheme-relative reference, for example a host allowlist or denylist that compares `parse(url).host` or uses `fast-uri.equal`, can be steered past the check with a percent-encoded uppercase octet. Because a hostname is case-insensitive in DNS and HTTP routing, the evading spelling reaches the same host the check meant to gate, so the effect is check evasion rather than reaching a different registrable host.\n\n### Patches\n\nUpgrade to `fast-uri` 4.1.5, 3.1.8, or 2.4.7.\n\n### Workarounds\n\nCompare hosts case-insensitively (lowercase the parsed host before any allowlist or denylist decision), or avoid making case-sensitive host decisions on scheme-relative input until upgrading.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fast-uri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2.4.7"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fast-uri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "3.1.8"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "npm",
      "name" : "fast-uri"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.0.0"
      }, {
        "fixed" : "4.1.5"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/security/advisories/GHSA-hrr3-gc8f-f4qj"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-86472"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/commit/5dabb86732aa2a7655e258719970e61e12b6b4d1"
  }, {
    "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/v2.4.7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/releases/tag/v3.1.8"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fastify/fast-uri/releases/tag/v4.1.5"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-178" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-29T23:54:25Z",
    "nvd_published_at" : "2026-09-15T11:17:12Z"
  }
}