CVE-2026-2782
📋 TL;DR
This CVE describes a privilege escalation vulnerability in Firefox's Netmonitor component that allows attackers to gain elevated privileges on affected systems. It affects Firefox versions below 148 and Firefox ESR versions below 140.8. Users running these vulnerable versions are at risk of having their browser security compromised.
💻 Affected Systems
- Mozilla Firefox
- Mozilla Firefox ESR
📦 What is this software?
Firefox by Mozilla
Firefox by Mozilla
Thunderbird by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise where attacker gains administrative privileges, installs malware, steals sensitive data, and maintains persistent access.
Likely Case
Local privilege escalation allowing attacker to bypass browser sandbox, access local files, and execute arbitrary code with user privileges.
If Mitigated
Limited impact if browser runs with minimal privileges, but still potential for data theft and limited system access.
🎯 Exploit Status
Requires user to visit malicious website or interact with crafted content. No public exploit code available at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 148, Firefox ESR 140.8
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2026-13/
Restart Required: Yes
Instructions:
1. Open Firefox menu > Help > About Firefox. 2. Allow browser to check for updates. 3. Restart Firefox when prompted. 4. Verify version is now 148 or higher (or 140.8+ for ESR).
🔧 Temporary Workarounds
Disable Developer Tools
allTemporarily disable Firefox Developer Tools to remove Netmonitor component access
about:config
Set devtools.enabled to false
Disable JavaScript
allDisable JavaScript to prevent web-based exploitation vectors
about:config
Set javascript.enabled to false
🧯 If You Can't Patch
- Restrict browser to trusted websites only using enterprise policies
- Run Firefox with minimal user privileges and enable sandboxing features
🔍 How to Verify
Check if Vulnerable:
Open Firefox, go to Help > About Firefox, check if version is below 148 (or below 140.8 for ESR)Check Version:
firefox --version (Linux) or check About Firefox menuVerify Fix Applied:
After update, verify version shows 148 or higher (or 140.8+ for ESR) in About Firefox📡 Detection & Monitoring
Log Indicators:
- Unusual Netmonitor component activity
- Privilege escalation attempts in system logs
- Firefox crash reports with privilege-related errors
Network Indicators:
- Connections to suspicious domains coinciding with Firefox Netmonitor usage
SIEM Query:
source="firefox.log" AND ("netmonitor" OR "privilege") AND severity=HIGH