CVE-2021-23962 – CVE-2021-23962 is a use-after-poison vulnerabil... (How to Fix)

Q: How do I fix CVE-2021-23962?

1. Open Firefox 2. Click menu (three horizontal lines) → Help → About Firefox 3. Firefox will automatically check for and download updates 4. Click 'Restart to update Firefox' when prompted

Q: What is the severity of CVE-2021-23962?

CVE-2021-23962 has a CVSS score of 8.8 (HIGH). CVE-2021-23962 is a use-after-poison vulnerability in Firefox's '<RowCountChanged>' method that could lead to memory corruption and potentially exploitable crashes. Attackers could exploit this to execute arbitrary code or cause denial of service. This affects Firefox users running versions before 85.

📋 TL;DR

CVE-2021-23962 is a use-after-poison vulnerability in Firefox's '<RowCountChanged>' method that could lead to memory corruption and potentially exploitable crashes. Attackers could exploit this to execute arbitrary code or cause denial of service. This affects Firefox users running versions before 85.

💻 Affected Systems

Products:

Mozilla Firefox

Versions: All versions < 85

Operating Systems: Windows, macOS, Linux, Android, iOS

Default Config Vulnerable: ⚠️ Yes

Notes: All default configurations of affected Firefox versions are vulnerable

📦 What is this software?

Firefox by Mozilla

View all CVEs affecting Firefox →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution allowing attackers to take full control of the affected system

🟠

Likely Case

Browser crash leading to denial of service and potential data loss

🟢

If Mitigated

No impact if Firefox is updated to version 85 or later

🌐 Internet-Facing: HIGH - Web browsers are directly exposed to malicious web content

🏢 Internal Only: MEDIUM - Internal users could be targeted via malicious internal sites or emails

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires user interaction (visiting malicious website or opening malicious content)

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Firefox 85

Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2021-03/

Restart Required: Yes

Instructions:

1. Open Firefox
2. Click menu (three horizontal lines) → Help → About Firefox
3. Firefox will automatically check for and download updates
4. Click 'Restart to update Firefox' when prompted

🔧 Temporary Workarounds

Disable JavaScript

all

Temporarily disable JavaScript to prevent exploitation via malicious web content

about:config → javascript.enabled → false

Use alternative browser

all

Switch to an updated alternative browser until Firefox can be patched

🧯 If You Can't Patch

Restrict web browsing to trusted sites only
Implement network filtering to block malicious domains and content

🔍 How to Verify

Check if Vulnerable:

Check Firefox version: about:support → Application Basics → Version

Check Version:

firefox --version

Verify Fix Applied:

Verify Firefox version is 85.0 or higher

📡 Detection & Monitoring

Log Indicators:

Firefox crash reports with memory corruption signatures
Unexpected browser termination events

Network Indicators:

Connections to known malicious domains serving exploit code

SIEM Query:

source="firefox.logs" AND (event="crash" OR event="termination") AND version<85

📊 Metadata

CVE ID: CVE-2021-23962

CVSS v3 Score: 8.8 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Published: February 26, 2021

Last Updated: November 21, 2024

🔗 References

https://bugzilla.mozilla.org/show_bug.cgi?id=1677194 Issue Tracking,Permissions Required,Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-03/ Release Notes,Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1677194 Issue Tracking,Permissions Required,Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-03/ Release Notes,Vendor Advisory

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