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CVE-2021-21392

Estado: ModificadaMedia (6.3)—

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.28.0 requests to user provided domains were not restricted to external IP addresses when transitional IPv6 addresses were used. Outbound requests to federation, identity servers, when calculating the key validity for third-party invite events, sending push notifications, and generating URL previews are affected. This could cause Synapse to make requests to internal infrastructure on dual-stack networks. See referenced GitHub security advisory for details and workarounds.

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).

Tecnologías afectadas (2)

Fedoraproject — FedoraMatrix — Synapse

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2021-21392",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 4.9,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:M/Au:S/C:P/I:P/A:N",
          "authentication": "SINGLE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "MEDIUM",
          "availabilityImpact": "NONE",
          "confidentialityImpact": "PARTIAL"
        },
        "acInsufInfo": false,
        "impactScore": 4.9,
        "baseSeverity": "MEDIUM",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 6.8,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": true
      }
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    "cvssMetricV31": [
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          "version": "3.1",
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          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:H/A:N",
          "integrityImpact": "HIGH",
          "userInteraction": "REQUIRED",
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          "integrityImpact": "HIGH",
          "userInteraction": "REQUIRED",
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      "source": "security-advisories@github.com",
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          "vendor": "matrix-org",
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          "versions": [
            {
              "status": "affected",
              "version": "< 1.28.0"
            }
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        }
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  ],
  "published": "2021-04-12T22:15:13.147",
  "references": [
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      "url": "https://github.com/matrix-org/synapse/pull/9240",
      "tags": [
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    },
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    },
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
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      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-601"
        }
      ]
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    {
      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
        {
          "lang": "en",
          "value": "CWE-601"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.28.0 requests to user provided domains were not restricted to external IP addresses when transitional IPv6 addresses were used. Outbound requests to federation, identity servers, when calculating the key validity for third-party invite events, sending push notifications, and generating URL previews are affected. This could cause Synapse to make requests to internal infrastructure on dual-stack networks. See referenced GitHub security advisory for details and workarounds."
    },
    {
      "lang": "es",
      "value": "Synapse es un servidor doméstico de referencia de Matrix escrito en python (paquete pypi matrix-synapse).&#xa0;Matrix es un ecosistema para VoIP y mensajería instantánea federada abierta.&#xa0;En Synapse, versiones anteriores a 1.28.0, las peticiones a los dominios proporcionados por el usuario no estaban restringidas a direcciones IP externas cuando se usaban direcciones IPv6 de transición.&#xa0;Las peticiones salientes a la federación, los servidores de identidad, al calcular la validez de la clave para eventos de invitación de terceros, el envío de notificaciones push y la generación de vistas previas de URL están afectadas.&#xa0;Esto podría causar que Synapse realice peticiones a la infraestructura interna en redes de doble pila.&#xa0;Consulte el aviso de seguridad de GitHub al que se hace referencia para obtener detalles y soluciones"
    }
  ],
  "lastModified": "2026-06-17T03:35:28.643",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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              "criteria": "cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*",
              "vulnerable": true,
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              "versionEndExcluding": "1.28.0"
            }
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            }
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          "operator": "OR"
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  "sourceIdentifier": "security-advisories@github.com"
}