CVE-2026-2764
📋 TL;DR
This CVE describes a use-after-free vulnerability in Firefox's JavaScript JIT compiler that could allow arbitrary code execution. It affects Firefox versions below 148 and Firefox ESR versions below 115.33 or 140.8. Attackers could exploit this to execute malicious code in the browser context.
💻 Affected Systems
- Mozilla Firefox
- Mozilla Firefox ESR
📦 What is this software?
Firefox by Mozilla
Firefox by Mozilla
Firefox by Mozilla
Thunderbird by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full system compromise, data theft, or ransomware deployment
Likely Case
Browser compromise allowing session hijacking, credential theft, or malware installation
If Mitigated
Limited impact with proper sandboxing and exploit mitigations in place
🎯 Exploit Status
JIT vulnerabilities typically require sophisticated exploitation but can be weaponized once understood
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 148, Firefox ESR 115.33, 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 automatic update to complete. 3. Restart Firefox when prompted. 4. Verify version is 148 or higher (or ESR 115.33/140.8 or higher).
🔧 Temporary Workarounds
Disable JavaScript
allTemporarily disable JavaScript execution in Firefox
about:config > javascript.enabled = false
Use Content Security Policy
allImplement strict CSP headers to limit script execution
Content-Security-Policy: script-src 'self'
🧯 If You Can't Patch
- Isolate vulnerable browsers using network segmentation
- Implement application allowlisting to block Firefox execution
🔍 How to Verify
Check if Vulnerable:
Check Firefox version in menu > Help > About FirefoxCheck Version:
firefox --versionVerify Fix Applied:
Confirm version is Firefox 148+ or ESR 115.33+/140.8+📡 Detection & Monitoring
Log Indicators:
- Firefox crash reports with JIT-related stack traces
- Unexpected browser process termination
Network Indicators:
- Unusual outbound connections from browser process
- Suspicious JavaScript payloads in web traffic
SIEM Query:
process_name="firefox.exe" AND (event_id=1000 OR event_id=1001) AND stack_contains="js::jit"🔗 References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2012608
- https://www.mozilla.org/security/advisories/mfsa2026-13/
- https://www.mozilla.org/security/advisories/mfsa2026-14/
- https://www.mozilla.org/security/advisories/mfsa2026-15/
- https://www.mozilla.org/security/advisories/mfsa2026-16/
- https://www.mozilla.org/security/advisories/mfsa2026-17/
