CVE-2025-1012
📋 TL;DR
A race condition during concurrent delazification in Mozilla products could lead to use-after-free vulnerabilities, potentially allowing attackers to execute arbitrary code or crash applications. This affects Firefox, Firefox ESR, and Thunderbird users running outdated versions. The vulnerability requires user interaction such as visiting a malicious website.
💻 Affected Systems
- Firefox
- Firefox ESR
- Thunderbird
📦 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 complete system compromise, data theft, or installation of persistent malware.
Likely Case
Application crash (denial of service) or limited memory corruption that could be leveraged for further exploitation.
If Mitigated
Minimal impact with proper patching and security controls; crashes may occur but without code execution.
🎯 Exploit Status
Exploitation requires race condition timing and memory manipulation. No public exploits known at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 135, Firefox ESR 115.20, Firefox ESR 128.7, Thunderbird 128.7, Thunderbird 135
Vendor Advisory: https://www.mozilla.org/security/advisories/
Restart Required: Yes
Instructions:
1. Open Firefox/Thunderbird. 2. Click menu → Help → About Firefox/Thunderbird. 3. Allow automatic update download and installation. 4. Restart the application when prompted.
🔧 Temporary Workarounds
Disable JavaScript
allPrevents exploitation by blocking JavaScript execution, which is required to trigger the race condition.
about:config → javascript.enabled = false
Use NoScript Extension
allSelectively block JavaScript on untrusted websites while maintaining functionality on trusted sites.
Install NoScript from addons.mozilla.org
🧯 If You Can't Patch
- Restrict browser usage to trusted websites only
- Implement application whitelisting to prevent execution of malicious code
🔍 How to Verify
Check if Vulnerable:
Check version in browser: Firefox/Thunderbird → Help → About. Compare against affected versions.Check Version:
firefox --version or thunderbird --versionVerify Fix Applied:
Confirm version is equal to or greater than patched versions: Firefox ≥135, Firefox ESR ≥115.20 or ≥128.7, Thunderbird ≥128.7 or ≥135.📡 Detection & Monitoring
Log Indicators:
- Application crash logs with memory access violations
- Unexpected process termination in system logs
Network Indicators:
- Unusual outbound connections after visiting websites
- Traffic to known malicious domains
SIEM Query:
source="firefox.log" OR source="thunderbird.log" AND ("crash" OR "segfault" OR "access violation")🔗 References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1939710
- https://www.mozilla.org/security/advisories/mfsa2025-07/
- https://www.mozilla.org/security/advisories/mfsa2025-08/
- https://www.mozilla.org/security/advisories/mfsa2025-09/
- https://www.mozilla.org/security/advisories/mfsa2025-10/
- https://www.mozilla.org/security/advisories/mfsa2025-11/
- https://lists.debian.org/debian-lts-announce/2025/02/msg00005.html
- https://lists.debian.org/debian-lts-announce/2025/02/msg00006.html
