CVE-2021-23955Public exploitNetwork attack vector

Cross-tab clickjacking via stale pointer lock

Published Feb 26, 2021 · Updated Aug 3, 2024

Clickjacking in Mozilla Firefox before 85 allows remote attackers to redirect a user's mouse input across browser tabs via a crafted page. After requestPointerLock is denied, the requesting content process fails to notify the parent process, which continues dispatching mouse events to that process after focus moves to another tab. Exploitation requires a user to open the crafted page and interact with another tab, allowing clicks intended for a visible site to reach attacker-controlled content.

CVSS severity6.1
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

Clickjacking in Mozilla Firefox before 85 allows remote attackers to redirect a user's mouse input across browser tabs via a crafted page. After requestPointerLock is denied, the requesting content process fails to notify the parent process, which continues dispatching mouse events to that process after focus moves to another tab. Exploitation requires a user to open the crafted page and interact with another tab, allowing clicks intended for a visible site to reach attacker-controlled content.

The record

CVE
CVE-2021-23955
Published
Feb 26, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-1021, T1189
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

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-1021Improper Restriction of Rendered UI Layers or Frames
T1189Drive-by Compromise

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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