CVE-2026-27466
Bigbluebutton ≤ 3.0.22
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:LSummary
CVE-2026-27466 is a high-severity Exposure of Resource to Wrong Sphere (CWE-668) vulnerability in Bigbluebutton Bigbluebutton. Its CVSS base score is 7.2 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Cloud Instance Metadata API (T1552.005); ranked at the 33th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-27466 affects BigBlueButton, an open-source virtual classroom platform, specifically versions 3.0.21 and below. The vulnerability stems from instructions in the official "Server Customization" documentation for enabling ClamAV as a presentation file scanner. These instructions configure a flawed command that exposes ClamAV daemon (clamd) ports 3310 and 7357 to the internet, enabling denial-of-service attacks. Additionally, the setup mounts the /var/bigbluebutton directory with write permissions into the Docker container, potentially exposing it to future clamd vulnerabilities. Users are unaffected unless they explicitly followed these optional documentation steps.
A remote attacker with network access can exploit this by sending complex or large documents to the exposed clamd ports, wasting server resources or shutting down the clamd process entirely. The CVSS v3.1 base score of 7.2 (AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:L) reflects high severity due to low attack complexity, no required privileges or user interaction, and changed scope impacting availability with low confidentiality impact. Enabling UFW during installation provides no protection, as Docker routes container traffic through the NAT table, bypassing UFW rules in the filter table.
The issue has been addressed in BigBlueButton version 3.0.22. The GitHub security advisory (GHSA-wmhx-qw2p-w6gc) and associated commit (f3d33d94a9682e87c7d41f55700b19d61e1ab8b4) detail the fix, emphasizing that administrators should upgrade and avoid following the vulnerable documentation instructions. The clamd documentation itself warns against exposing these ports to untrusted networks.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-7723
Vulnerability Data
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…
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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.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 8 hardening rules · 7 OS baselines
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Mitigating Controls (NIST 800-53 r5) AI
Access enforcement directly stops resources from being reachable by actors outside the intended control sphere.
Information flow enforcement structurally prevents unintended cross-sphere data or resource exposure.
Least privilege reduces the set of actors that can reach a resource, limiting wrong-sphere exposure.
Security attributes enable correct sphere assignment and subsequent enforcement decisions.
Boundary protection at interfaces prevents resources from being exposed outside authorized spheres.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Enforcing least-privilege authorizations directly prevents resources from being exposed outside their intended control sphere.
Network segmentation and unauthorized-access protections reduce the chance of resources being reachable by the wrong sphere.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Placing systems of differing trust levels into separate domains prevents resources from being placed in a sphere where they are reachable by unintended actors.
Requiring owners to manage the full asset life cycle and remove assets from the inventory upon secure disposal helps prevent resources from being inadvertently exposed outside their intended security sphere.
Hardening callouts derived
Configuration rules from DISA STIG baselines that bear on weaknesses of the type cited by this CVE. Each rule is shown with the relationship its mapping actually records, against the CWE it was authored against. Derived via CVE→CWE over `controls_xwalks` (authoritative rows only; rows rated `none` are excluded).
Oracle Linux 8 (2 rules)
- V-248827 OL 8 must not have the rsh-server package installed. prevents CWE-668
- V-248823 OL 8 must not have the telnet-server package installed. prevents CWE-668
RHEL 7 (1 rule)
- V-204442 The Red Hat Enterprise Linux operating system must not have the rsh-server package installed. prevents CWE-668
Windows 10 (1 rule)
- V-220967 The Debug programs user right must only be assigned to the Administrators group. prevents CWE-668
Windows 11 (1 rule)
- V-253490 The "Debug programs" user right must only be assigned to the Administrators group. prevents CWE-668
Windows Server 2016 (1 rule)
- V-225079 The Debug programs user right must only be assigned to the Administrators group. prevents CWE-668
Windows Server 2019 (1 rule)
- V-205757 Windows Server 2019 Debug programs: user right must only be assigned to the Administrators group. prevents CWE-668
Windows Server 2022 (1 rule)
- V-254500 Windows Server 2022 debug programs user right must only be assigned to the Administrators group. prevents CWE-668