CVE-2026-2776
📋 TL;DR
This CVE describes a sandbox escape vulnerability in Firefox's Telemetry component due to incorrect boundary conditions. Attackers could potentially break out of browser security sandboxes to execute arbitrary code. Affected users include those running Firefox versions below 148, Firefox ESR below 115.33, or Firefox ESR below 140.8.
💻 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
Complete system compromise allowing attackers to execute arbitrary code with the privileges of the Firefox process, potentially leading to data theft, ransomware deployment, or persistent backdoor installation.
Likely Case
Limited sandbox escape allowing attackers to access restricted system resources or execute code within the browser's security context, potentially leading to credential theft or further exploitation.
If Mitigated
Attack contained within browser sandbox with minimal impact if proper security controls and updated versions are in place.
🎯 Exploit Status
Exploitation requires user interaction (visiting malicious website) but no authentication. The boundary condition vulnerability suggests memory corruption exploitation.
🛠️ 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 Firefox to check for updates. 3. If updates are available, click 'Restart to update'. 4. For enterprise deployments, use Firefox ESR deployment tools or update through standard software distribution channels.
🔧 Temporary Workarounds
Disable Telemetry
allDisables the vulnerable Telemetry component to prevent exploitation
about:config
Set 'toolkit.telemetry.enabled' to false
Set 'datareporting.healthreport.uploadEnabled' to false
Enable Enhanced Sandboxing
allStrengthens browser sandbox protections to limit impact if exploited
about:config
Set 'security.sandbox.content.level' to 3 or higher
🧯 If You Can't Patch
- Implement network filtering to block access to untrusted websites
- Use application whitelisting to restrict execution of unauthorized processes
🔍 How to Verify
Check if Vulnerable:
Check Firefox version in menu > Help > About Firefox. If version is below 148 (or ESR below specified versions), system is vulnerable.Check Version:
firefox --versionVerify Fix Applied:
After update, verify version shows Firefox 148 or higher, or Firefox ESR 115.33/140.8 or higher.📡 Detection & Monitoring
Log Indicators:
- Unusual process creation from Firefox
- Sandbox violation events in system logs
- Crash reports from Firefox with memory corruption signatures
Network Indicators:
- Connections to known malicious domains from Firefox process
- Unusual outbound traffic patterns
SIEM Query:
process_name="firefox.exe" AND (event_id=4688 OR parent_process_name="firefox.exe")🔗 References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2015266
- 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/
