Stored XSS via unescaped meeting name
Published Aug 20, 2026 · Updated Aug 20, 2026
Stored XSS in screenshare playback in BigBlueButton before 3.0.29 allows remote authenticated users to run script via a crafted meeting name. The record-and-playback/screenshare/playback/index.html.erb template inserts meetingName into the page title and header without HTML escaping; the fix wraps both outputs in CGI.escapeHTML. Exploitation requires low-privileged access to create or rename a meeting and a second user to replay the recording, yielding script execution in that viewer's browser session rather than server-side code execution.
Summary
What happened
Stored XSS in screenshare playback in BigBlueButton before 3.0.29 allows remote authenticated users to run script via a crafted meeting name. The record-and-playback/screenshare/playback/index.html.erb template inserts meetingName into the page title and header without HTML escaping; the fix wraps both outputs in CGI.escapeHTML. Exploitation requires low-privileged access to create or rename a meeting and a second user to replay the recording, yielding script execution in that viewer's browser session rather than server-side code execution.
The record
- CVE
- CVE-2026-55491
- Published
- Aug 20, 2026
- Updated
- Aug 20, 2026
- Vendor
- BigBlueButton Inc.
- Product
- BigBlueButton
- Classifications
- CWE-79, T1059.007
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 20, 2026CVE publishedPublication date reported by the CVE source.
- Aug 20, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 3.0.29
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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