CVE-2021-29976
📋 TL;DR
This CVE describes memory safety bugs in Mozilla's code shared between Firefox and Thunderbird that could lead to memory corruption. With sufficient effort, attackers could potentially exploit these vulnerabilities to execute arbitrary code on affected systems. Users running vulnerable versions of Firefox, Firefox ESR, or Thunderbird are at risk.
💻 Affected Systems
- Mozilla Firefox
- Mozilla Firefox ESR
- Mozilla Thunderbird
📦 What is this software?
Firefox by Mozilla
Firefox Esr 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
Application crashes (denial of service) or limited memory corruption that could be leveraged for further exploitation.
If Mitigated
Minimal impact if systems are patched, isolated, or have additional security controls like application sandboxing.
🎯 Exploit Status
Memory corruption vulnerabilities require sophisticated exploitation techniques but could be triggered via malicious web content.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Thunderbird 78.12+, Firefox ESR 78.12+, Firefox 90+
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2021-28/
Restart Required: Yes
Instructions:
1. Open the affected application. 2. Go to Help > About. 3. Allow the application to check for and install updates. 4. Restart the application when prompted.
🔧 Temporary Workarounds
Disable JavaScript
allTemporarily reduces attack surface by disabling JavaScript execution.
Use Application Sandboxing
allRun browser in sandboxed environment to limit potential damage.
🧯 If You Can't Patch
- Network segmentation to isolate vulnerable systems
- Implement web content filtering to block malicious sites
🔍 How to Verify
Check if Vulnerable:
Check application version in Help > About menu.Check Version:
firefox --version or thunderbird --versionVerify Fix Applied:
Confirm version is Thunderbird 78.12+, Firefox ESR 78.12+, or Firefox 90+.📡 Detection & Monitoring
Log Indicators:
- Application crash logs
- Memory access violation errors
Network Indicators:
- Unusual outbound connections from browser processes
SIEM Query:
source="*firefox*" OR source="*thunderbird*" AND (event="crash" OR event="segfault")🔗 References
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=1700895%2C1703334%2C1706910%2C1711576%2C1714391
- https://security.gentoo.org/glsa/202202-03
- https://security.gentoo.org/glsa/202208-14
- https://www.mozilla.org/security/advisories/mfsa2021-28/
- https://www.mozilla.org/security/advisories/mfsa2021-29/
- https://www.mozilla.org/security/advisories/mfsa2021-30/
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=1700895%2C1703334%2C1706910%2C1711576%2C1714391
- https://security.gentoo.org/glsa/202202-03
- https://security.gentoo.org/glsa/202208-14
- https://www.mozilla.org/security/advisories/mfsa2021-28/
- https://www.mozilla.org/security/advisories/mfsa2021-29/
- https://www.mozilla.org/security/advisories/mfsa2021-30/
