Vulnerability-Lookup

GHSA-V2HH-GCRM-F6HX

Vulnerability from github – Published: 2026-07-21 22:08 – Updated: 2026-07-21 22:08

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

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{
  "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"
}

CVE-2026-16221 (GCVE-0-2026-16221)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:08 – Updated: 2026-07-20 13:53

Title

fast-uri vulnerable to host confusion via literal backslash authority delimiter

Summary

Impact: fast-uri versions from 2.3.1 through 4.1.0 (including the 3.x line up to 3.1.3 and the 2.x line up to 2.4.2) do not treat a literal backslash character (U+005C) as an authority delimiter. Node's native WHATWG URL parser, used by fetch, undici, and Node's http and https clients, normalizes the backslash to a forward slash for special schemes such as http, https, ws, wss, ftp, and file. As a result, the two parsers extract different hosts from the same input string. Applications that use fast-uri to enforce host-based policy such as allowlists, denylists, loopback or SSRF filtering, redirect validation, or outbound proxy routing before passing the same URL into Node's URL or fetch consumers can be steered to an unintended destination, including cloud metadata endpoints, loopback, or internal hosts. Patches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3. Workarounds: none.

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-20 13:53 UTC

CWE

CWE-436 - Interpretation Conflict

Assigner

openjs redhat root

References

2 references

URL	Tags
https://github.com/fastify/fast-uri/security/advi…
https://cna.openjsf.org/security-advisories.html

Impacted products

1 product

Vendor	Product	Version
fast-uri	fast-uri	Affected: 2.3.1 , < 2.4.3 (semver) Unaffected: 2.4.3 (semver) Affected: 3.0.0 , < 3.1.4 (semver) Unaffected: 3.1.4 (semver) Affected: 4.0.0 , < 4.1.1 (semver) Unaffected: 4.1.1 (semver)

Credits

rampage0010 mcollina UlisesGascon

Show details on NVD website

JSON

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Sightings

Author	Source	Type	Date	Other

Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
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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.

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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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