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CVE-2026-16221

Estado: AnalizadaAlta (7.5)—

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.

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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.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad de parseo diferencial (CWE-436) en fast-uri que permite eludir validaciones de hosts y SSRF filtering en aplicaciones web expuestas (AV:N, PR:N, UI:N), redirigiendo hacia endpoints internos, metadata o loopback; impacta SSRF (T1090) y potencial acceso a credenciales (T1552).

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network TrafficPrivileged Account ManagementLimit Access to Resource Over NetworkUpdate SoftwareActive Directory ConfigurationVulnerability Scanning

Tecnologías afectadas (1)

Openjsf — Fast-uri

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-16221",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-16221",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-07-20T13:53:31.279563Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "ce714d77-add3-4f53-aff5-83d477b104bb",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.5,
          "attackVector": "NETWORK",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 3.6,
        "exploitabilityScore": 3.9
      }
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  "affected": [
    {
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      "affectedData": [
        {
          "vendor": "fast-uri",
          "product": "fast-uri",
          "versions": [
            {
              "status": "affected",
              "version": "2.3.1",
              "lessThan": "2.4.3",
              "versionType": "semver"
            },
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              "version": "2.4.3",
              "versionType": "semver"
            },
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              "status": "affected",
              "version": "3.0.0",
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              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "3.1.4",
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            {
              "status": "affected",
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              "lessThan": "4.1.1",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "4.1.1",
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          "packageURL": "pkg:npm/fast-uri",
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  "published": "2026-07-19T15:16:49.027",
  "references": [
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      "url": "https://cna.openjsf.org/security-advisories.html",
      "tags": [
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      "source": "ce714d77-add3-4f53-aff5-83d477b104bb"
    },
    {
      "url": "https://github.com/fastify/fast-uri/security/advisories/GHSA-v2hh-gcrm-f6hx",
      "tags": [
        "Vendor Advisory"
      ],
      "source": "ce714d77-add3-4f53-aff5-83d477b104bb"
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  ],
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "ce714d77-add3-4f53-aff5-83d477b104bb",
      "description": [
        {
          "lang": "en",
          "value": "CWE-436"
        }
      ]
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  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "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. \n\nPatches: upgrade to fast-uri 4.1.1, 3.1.4, or 2.4.3.\n\nWorkarounds: none."
    }
  ],
  "lastModified": "2026-08-05T19:46:09.890",
  "configurations": [
    {
      "nodes": [
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          "negate": false,
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              "versionEndExcluding": "3.1.4",
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            },
            {
              "criteria": "cpe:2.3:a:openjsf:fast-uri:*:*:*:*:*:node.js:*:*",
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              "versionEndExcluding": "4.1.1",
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          "operator": "OR"
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  "sourceIdentifier": "ce714d77-add3-4f53-aff5-83d477b104bb"
}