CVE-2021-4143Public exploitNetwork attack vector

Participant-browser script execution via unescaped cursor username

Published Jan 19, 2022 · Updated Aug 3, 2024

Cross-site scripting in BigBlueButton before 2.4.0 allows remote attackers to execute script in participants' browsers via a crafted username. The bundled mconf ep_cursortrace fork renders an attendee username as shared-notes cursor markup without HTML neutralization. Execution requires another participant to view shared notes in the same meeting, and the resulting access remains within that participant's browser context.

CVSS severity6.1
Medium
EPSS probability0.89%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in BigBlueButton before 2.4.0 allows remote attackers to execute script in participants' browsers via a crafted username. The bundled mconf ep_cursortrace fork renders an attendee username as shared-notes cursor markup without HTML neutralization. Execution requires another participant to view shared notes in the same meeting, and the resulting access remains within that participant's browser context.

The record

CVE
CVE-2021-4143
Published
Jan 19, 2022
Updated
Aug 3, 2024
Vendor
BigBlueButton Inc.
Product
BigBlueButton
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 19, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record 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.

  1. Affected versionversion=unspecified <2.4.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

BigBlueButton Inc. · BigBlueButtonversion=unspecified <2.4.0

Published CVSS scores

8.1huntr.devCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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