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CVE-2025-3909

Estado: ModificadaAlta (8.1)—

Thunderbird's handling of the X-Mozilla-External-Attachment-URL header can be exploited to execute JavaScript in the file:/// context. By crafting a nested email attachment (message/rfc822) and setting its content type to application/pdf, Thunderbird may incorrectly render it as HTML when opened, allowing the embedded JavaScript to run without requiring a file download. This behavior relies on Thunderbird auto-saving the attachment to /tmp and linking to it via the file:/// protocol, potentially enabling JavaScript execution as part of the HTML. This vulnerability was fixed in Thunderbird 128.10.1 and Thunderbird 138.0.1.

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.

UI:R (interacción del usuario al abrir email) con ejecución de JavaScript en contexto file:///; impacto en lectura de datos locales accesibles desde /tmp.

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

Restrict Web-Based ContentExecution PreventionBehavior Prevention on EndpointDisable or Remove Feature or ProgramApplication Isolation and SandboxingExploit Protection

Tecnologías afectadas (1)

Mozilla — Thunderbird

CWE

Referencias

JSON original (NVD)

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          "options": [
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      "value": "Thunderbird's handling of the X-Mozilla-External-Attachment-URL header can be exploited to execute JavaScript in the file:/// context. By crafting a nested email attachment (message/rfc822) and setting its content type to application/pdf, Thunderbird may incorrectly render it as HTML when opened, allowing the embedded JavaScript to run without requiring a file download. This behavior relies on Thunderbird auto-saving the attachment to /tmp and linking to it via the file:/// protocol, potentially enabling JavaScript execution as part of the HTML. This vulnerability was fixed in Thunderbird 128.10.1 and Thunderbird 138.0.1."
    },
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      "value": "La gestión que Thunderbird hace del encabezado X-Mozilla-External-Attachment-URL puede explotarse para ejecutar JavaScript en el contexto file:///. Al manipular un archivo adjunto de correo electrónico anidado (message/rfc822) y configurar su tipo de contenido como application/pdf, Thunderbird puede representarlo incorrectamente como HTML al abrirlo, lo que permite que el JavaScript incrustado se ejecute sin necesidad de descargar el archivo. Este comportamiento se basa en que Thunderbird guarda automáticamente el archivo adjunto en /tmp y lo enlaza mediante el protocolo file:///, lo que podría permitir la ejecución de JavaScript como parte del HTML. Esta vulnerabilidad afecta a Thunderbird versiones anteriores a la 128.10.1 y a la 138.0.1."
    }
  ],
  "lastModified": "2026-06-17T09:20:54.643",
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