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CVE-2026-27466

Estado: AnalizadaAlta (8.2)—

BigBlueButton is an open-source virtual classroom. In versions 3.0.21 and below, the official documentation for "Server Customization" on Support for ClamAV as presentation file scanner contains instructions that leave a BBB server vulnerable for Denial of Service. The flawed command exposes both ports (3310 and 7357) to the internet. A remote attacker can use this to send complex or large documents to clamd and waste server resources, or shutdown the clamd process. The clamd documentation explicitly warns about exposing this port.

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Enabling ufw (ubuntu firewall) during install does not help, because Docker routes container traffic through the nat table, which is not managed or restricted by ufw. Rules installed by ufw in the filter table have no effect on docker traffic. In addition, the provided example also mounts /var/bigbluebutton with write permissions into the container, which should not be required. Future vulnerabilities in clamd may allow attackers to manipulate files in that folder. Users are unaffected unless they have opted in to follow the extra instructions from BigBlueButton's documentation. This issue has been fixed in version 3.0.22.

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 en servicio remoto expuesto (clamd en puerto 3310/7357) sin autenticación (PR:N, UI:N) explotable por red. T1499.004 (DoS de aplicación) por envío de documentos complejos. T1565.001 (corrupción de datos) por montaje con permisos de escritura en /var/bigbluebutton.

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 TrafficVulnerability ScanningRestrict File and Directory PermissionsPrivileged Account ManagementRemote Data StorageNetwork Segmentation

Tecnologías afectadas (1)

Bigbluebutton — Bigbluebutton

CWE

Referencias

JSON original (NVD)

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  "id": "CVE-2026-27466",
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      "lang": "en",
      "value": "BigBlueButton is an open-source virtual classroom. In versions 3.0.21 and below, the official documentation for \"Server Customization\" on Support for ClamAV as presentation file scanner contains instructions that leave a BBB server vulnerable for Denial of Service. The flawed command exposes both ports (3310 and 7357) to the internet. A remote attacker can use this to send complex or large documents to clamd and waste server resources, or shutdown the clamd process. The clamd documentation explicitly warns about exposing this port. Enabling ufw (ubuntu firewall) during install does not help, because Docker routes container traffic through the nat table, which is not managed or restricted by ufw. Rules installed by ufw in the filter table have no effect on docker traffic. In addition, the provided example also mounts /var/bigbluebutton with write permissions into the container, which should not be required. Future vulnerabilities in clamd may allow attackers to manipulate files in that folder. Users are unaffected unless they have opted in to follow the extra instructions from BigBlueButton's documentation. This issue has been fixed in version 3.0.22."
    },
    {
      "lang": "es",
      "value": "BigBlueButton es un aula virtual de código abierto. En las versiones 3.0.21 e inferiores, la documentación oficial para 'Personalización del Servidor' en Soporte para ClamAV como escáner de archivos de presentación contiene instrucciones que dejan un servidor BBB vulnerable a la denegación de servicio. El comando defectuoso expone ambos puertos (3310 y 7357) a internet. Un atacante remoto puede usar esto para enviar documentos complejos o grandes a clamd y malgastar recursos del servidor, o apagar el proceso clamd. La documentación de clamd advierte explícitamente sobre la exposición de este puerto. Habilitar ufw (cortafuegos de ubuntu) durante la instalación no ayuda, porque Docker enruta el tráfico del contenedor a través de la tabla nat, la cual no es gestionada ni restringida por ufw. Las reglas instaladas por ufw en la tabla de filtros no tienen efecto en el tráfico de docker. Además, el ejemplo proporcionado también monta /var/bigbluebutton con permisos de escritura en el contenedor, lo cual no debería ser necesario. Futuras vulnerabilidades en clamd pueden permitir a los atacantes manipular archivos en esa carpeta. Los usuarios no se ven afectados a menos que hayan optado por seguir las instrucciones adicionales de la documentación de BigBlueButton. Este problema ha sido solucionado en la versión 3.0.22."
    }
  ],
  "lastModified": "2026-06-17T10:27:11.930",
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