CVE-2026-2758
📋 TL;DR
A use-after-free vulnerability in Firefox's JavaScript garbage collector component allows attackers to execute arbitrary code by manipulating memory after it has been freed. This affects Firefox versions below 148, Firefox ESR below 115.33, and Firefox ESR below 140.8. Users visiting malicious websites could have their systems compromised.
💻 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 crash or arbitrary code execution within browser context, potentially leading to credential theft or malware installation.
If Mitigated
Limited impact with proper browser sandboxing and security controls, potentially just browser crash.
🎯 Exploit Status
Use-after-free vulnerabilities typically require precise memory manipulation but are commonly exploited in browser attacks.
🛠️ 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 browser to check for updates. 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 to prevent exploitation
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
- Restrict browser usage to trusted websites only
- Implement application whitelisting to prevent unauthorized code 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:
- Browser crash reports with memory access violations
- Unusual JavaScript execution patterns
Network Indicators:
- Requests to known malicious domains with JavaScript payloads
SIEM Query:
source="firefox.log" AND ("access violation" OR "segmentation fault")🔗 References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2009608
- 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/
