CVE-2021-23955 in Firefox
Summary
by MITRE • 02/26/2021
The browser could have been confused into transferring a pointer lock state into another tab, which could have lead to clickjacking attacks. This vulnerability affects Firefox < 85.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 08/09/2025
The vulnerability identified as CVE-2021-23955 represents a critical cross-tab pointer lock state transfer issue within the Firefox browser implementation. This flaw stems from inadequate state management between browser tabs, specifically concerning the pointer lock API functionality that allows web applications to capture mouse movements and lock them to a specific element. The vulnerability arises when the browser fails to properly isolate pointer lock states between different tab contexts, creating a scenario where pointer lock information can be inadvertently transferred from one tab to another. This cross-tab state leakage creates a significant security risk as it enables malicious web applications to manipulate user interactions across different browsing contexts. The flaw particularly affects Firefox versions prior to 85, where the browser's tab isolation mechanisms were insufficient to prevent such state contamination. This issue directly impacts the browser's ability to maintain proper security boundaries between separate browsing contexts, potentially allowing attackers to exploit the misbehavior in ways that compromise user interaction integrity.
The technical implementation flaw occurs at the browser engine level where the pointer lock API state management does not adequately enforce tab-specific boundaries. When a user interacts with a web page that requests pointer lock functionality, the browser should maintain this state exclusively within that tab's context. However, in affected Firefox versions, the pointer lock state can be transferred or shared between tabs, creating an unintended interaction pattern. This behavior violates the fundamental security principle of process isolation and tab sandboxing that modern browsers implement to prevent cross-site scripting and user interface manipulation attacks. The vulnerability specifically relates to the browser's handling of the Pointer Lock API which is designed to provide immersive experiences for applications like games or drawing tools, but becomes dangerous when the lock state can be transferred between unrelated browsing contexts. This flaw essentially allows a malicious tab to inherit the pointer lock state from another tab, potentially enabling sophisticated clickjacking attacks where user interactions are redirected or manipulated without proper user awareness or consent.
The operational impact of this vulnerability extends beyond simple pointer lock confusion, creating a potential attack vector for sophisticated clickjacking scenarios that could compromise user security and privacy. Attackers could exploit this flaw by creating malicious web pages that leverage the pointer lock state transfer to manipulate user interactions across different tabs, potentially redirecting clicks to unintended targets or capturing user input in ways that bypass normal browser security controls. The vulnerability enables an attacker to perform actions that would normally be restricted to the original tab, potentially leading to unauthorized data access, form submissions, or navigation to malicious sites. Users who maintain multiple tabs open simultaneously become particularly vulnerable as the attack can occur without their knowledge or explicit consent, since the pointer lock state transfer happens automatically within the browser's internal state management. This creates a persistent security risk where even benign-looking websites could potentially exploit the vulnerability to conduct malicious activities. The impact is especially concerning in environments where users interact with sensitive applications across multiple tabs, as the attack could be used to manipulate user input in critical applications or banking interfaces.
Mitigation strategies for CVE-2021-23955 require immediate browser updates to version 85 or later where the pointer lock state management has been properly corrected. Users should ensure their Firefox installations are updated to the latest version to prevent exploitation of this vulnerability. Organizations should implement browser security policies that enforce automatic updates and monitor for vulnerable browser versions in their environments. Security teams should also consider implementing additional monitoring for suspicious pointer lock API usage patterns that could indicate exploitation attempts. The fix implemented in Firefox 85 addresses the core state management issue by strengthening tab isolation mechanisms for pointer lock functionality, ensuring that pointer lock states are properly confined to their originating tab contexts. This remediation aligns with security best practices outlined in the CWE catalog under CWE-691, which addresses inadequate protection of pointer lock API functionality. The solution also reflects principles from the MITRE ATT&CK framework, specifically addressing techniques related to user interface manipulation and credential access through browser-based attacks. Regular security assessments should verify that pointer lock API usage in web applications follows proper state management practices and that browser security configurations are optimized to prevent such cross-tab state transfer behaviors. System administrators should also consider implementing browser hardening measures that restrict pointer lock API access to trusted domains only, reducing the attack surface for potential exploitation of similar vulnerabilities.