CVE-2026-2762
📋 TL;DR
An integer overflow vulnerability in Firefox's JavaScript Standard Library component could allow attackers to execute arbitrary code or cause denial of service. This affects Firefox versions below 148 and Firefox ESR versions below 140.8. Users who visit malicious websites or open crafted content could be exploited.
💻 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
Remote code execution leading to complete system compromise, data theft, or ransomware deployment.
Likely Case
Browser crash (denial of service) or limited code execution within browser sandbox.
If Mitigated
Browser crash with no data loss if sandboxing holds, or exploit blocked by security controls.
🎯 Exploit Status
Exploitation requires user interaction (visiting malicious site). No public exploit code known.
🛠️ 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. 2. Click menu → Help → About Firefox. 3. Allow automatic update download and install. 4. Restart Firefox when prompted.
🔧 Temporary Workarounds
Disable JavaScript
allTemporarily disable JavaScript to prevent exploitation (breaks most websites).
about:config → javascript.enabled = false
Use NoScript Extension
allInstall NoScript to selectively block JavaScript on untrusted sites.
Install from https://addons.mozilla.org/firefox/addon/noscript/
🧯 If You Can't Patch
- Restrict browser use to trusted websites only.
- Implement network filtering to block known malicious domains.
🔍 How to Verify
Check if Vulnerable:
Check Firefox version: Menu → Help → About Firefox. If version is below 148 (or ESR below 140.8), system is vulnerable.Check Version:
firefox --versionVerify Fix Applied:
Confirm version is Firefox 148+ or Firefox ESR 140.8+ in About Firefox dialog.📡 Detection & Monitoring
Log Indicators:
- Browser crash logs with JavaScript-related errors
- Unexpected browser process termination
Network Indicators:
- Connections to suspicious domains followed by browser crashes
SIEM Query:
source="firefox.log" AND ("crash" OR "segfault") AND "javascript"