CVE-2026-27466: BigBlueButton is an open-source virtual classroom. In versions 3.0.21 and below, the official documentation for "Server Customization" on Support for ...

Description

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.

Metrics

CVSS 3.1

8.2/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H

EPSS Probability

0.40%

31.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-668

Affected Software

Vendor	Product	Versions
Bigbluebutton	Bigbluebutton	< 3.0.22

References

https://github.com/bigbluebutton/bigbluebutton/commit/f3d33d94a9682e87c7d41f55700b19d61e1ab8b4Patch
https://github.com/bigbluebutton/bigbluebutton/security/advisories/GHSA-wmhx-qw2p-w6gcExploit, Patch, Vendor Advisory

Timeline

Published: Feb 21, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-27466?

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.

How severe is CVE-2026-27466?

CVE-2026-27466 has a CVSS score of 8.2/10 (HIGH severity). The EPSS model estimates a 0.40% probability of exploitation in the next 30 days.

How do I fix CVE-2026-27466?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.