CVE-2021-23963Network attack vector

Active WebRTC sharing concealment via state overwrite

Published Feb 26, 2021 · Updated Aug 3, 2024

Permission-state corruption in Mozilla Firefox before 85 allows remote attackers to conceal active WebRTC sharing indicators via geolocation. The updateBrowserSharing path sets tab._sharingState.webRTC to null when geolocation sharing begins, removing tab, identity, and permission-list indicators while the global WebRTC indicator remains. Exploitation requires a user to grant WebRTC device or screen access and then grant geolocation access, leaving that sharing active but less visible.

CVSS severity4.3
Medium
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Permission-state corruption in Mozilla Firefox before 85 allows remote attackers to conceal active WebRTC sharing indicators via geolocation. The updateBrowserSharing path sets tab._sharingState.webRTC to null when geolocation sharing begins, removing tab, identity, and permission-list indicators while the global WebRTC indicator remains. Exploitation requires a user to grant WebRTC device or screen access and then grant geolocation access, leaving that sharing active but less visible.

The record

CVE
CVE-2021-23963
Published
Feb 26, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-281
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 26, 2021CVE 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=< 85

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=< 85

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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

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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 exploitUnconfirmed

Weakness, pattern, technique

CWE-281Improper Preservation of Permissions

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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