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CVE-2021-21333

Estado: ModificadaMedia (6.1)—

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 1.27.0, the notification emails sent for notifications for missed messages or for an expiring account are subject to HTML injection. In the case of the notification for missed messages, this could allow an attacker to insert forged content into the email. The account expiry feature is not enabled by default and the HTML injection is not controllable by an attacker. This is fixed in version 1.27.0.

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-2021-21333",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "version": "2.0",
          "baseScore": 2.6,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:H/Au:N/C:N/I:P/A:N",
          "authentication": "NONE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "HIGH",
          "availabilityImpact": "NONE",
          "confidentialityImpact": "NONE"
        },
        "acInsufInfo": false,
        "impactScore": 2.9,
        "baseSeverity": "LOW",
        "obtainAllPrivilege": false,
        "exploitabilityScore": 4.9,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": true
      }
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          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:H/A:N",
          "integrityImpact": "HIGH",
          "userInteraction": "REQUIRED",
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        "impactScore": 4,
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          "versions": [
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              "status": "affected",
              "version": "< 1.27.0"
            }
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  "published": "2021-03-26T20:15:11.953",
  "references": [
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      "source": "af854a3a-2127-422b-91ae-364da2661108"
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  "vulnStatus": "Modified",
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      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-74"
        }
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    },
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      "description": [
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          "lang": "en",
          "value": "CWE-79"
        }
      ]
    }
  ],
  "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 1.27.0, the notification emails sent for notifications for missed messages or for an expiring account are subject to HTML injection. In the case of the notification for missed messages, this could allow an attacker to insert forged content into the email. The account expiry feature is not enabled by default and the HTML injection is not controllable by an attacker. This is fixed in version 1.27.0."
    },
    {
      "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 1.27.0, los correos electrónicos de notificación enviados para notificaciones de mensajes perdidos o para una cuenta que vence están sujetos a una inyección de HTML.&#xa0;En el caso de la notificación de mensajes perdidos, esto podría permitir a un atacante insertar contenido forjado en el correo electrónico.&#xa0;La funcionalidad expiry de la cuenta no está habilitada por defecto y la inyección de HTML por un atacante no es controlable .&#xa0;Esto es corregido en la versión 1.27.0."
    }
  ],
  "lastModified": "2026-06-17T03:35:19.060",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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              "versionEndExcluding": "1.27.0"
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}