GHSA-V2HH-GCRM-F6HX

Vulnerability from github – Published: 2026-07-21 22:08 – Updated: 2026-07-21 22:08
VLAI
Summary
fast-uri vulnerable to host confusion via literal backslash authority delimiter
Details

Impact

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.

For 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.

Applications 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.

Patches

Upgrade to fast-uri v4.1.1, v3.1.4, or v2.4.3.

Workarounds

None. Upgrade to the patched version.

Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Show details on source website
To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.4.2"
      },
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.3.1"
            },
            {
              "fixed": "2.4.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.1.3"
      },
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.0"
            },
            {
              "fixed": "3.1.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.1.0"
      },
      "package": {
        "ecosystem": "npm",
        "name": "fast-uri"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "4.1.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-16221"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-436"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-21T22:08:28Z",
    "nvd_published_at": "2026-07-19T15:16:49Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\n`fast-uri` v4.1.0 and earlier do not treat a literal backslash (U+005C) as an authority delimiter. Node\u0027s native WHATWG `URL` (used by `fetch()`, `undici`, and Node\u0027s `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\u0027s 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\u0027s 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.",
  "id": "GHSA-v2hh-gcrm-f6hx",
  "modified": "2026-07-21T22:08:29Z",
  "published": "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "fast-uri vulnerable to host confusion via literal backslash authority delimiter"
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.