CVE-2020-26968
📋 TL;DR
This CVE describes memory safety bugs in Firefox, Firefox ESR, 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 Firefox versions below 83, Firefox ESR below 78.5, or Thunderbird below 78.5 are vulnerable.
💻 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 allowing attackers to take complete control of the affected system, install malware, steal data, or pivot to other systems.
Likely Case
Browser/application crashes (denial of service) or limited memory corruption that could be leveraged for information disclosure or further exploitation.
If Mitigated
No impact if systems are patched or if exploit attempts are blocked by security controls like application allowlisting or network filtering.
🎯 Exploit Status
Memory corruption bugs require sophisticated exploitation techniques, but successful exploitation could lead to arbitrary code execution without user authentication beyond visiting a malicious website or opening a malicious email.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox 83+, Firefox ESR 78.5+, Thunderbird 78.5+
Vendor Advisory: https://www.mozilla.org/security/advisories/mfsa2020-50/
Restart Required: Yes
Instructions:
1. Open the affected application (Firefox/Thunderbird). 2. Click the menu button (three horizontal lines). 3. Select Help > About Firefox/Thunderbird. 4. The application will automatically check for updates and prompt to install. 5. Restart the application when prompted.
🔧 Temporary Workarounds
Disable JavaScript
allTemporarily reduces attack surface by disabling JavaScript execution, which is commonly used to trigger memory corruption vulnerabilities.
In Firefox: about:config > javascript.enabled = false
Use Alternative Browser
allSwitch to an unaffected browser until patches can be applied.
🧯 If You Can't Patch
- Restrict network access to prevent browsers from accessing untrusted websites
- Implement application control to block execution of vulnerable browser versions
🔍 How to Verify
Check if Vulnerable:
Check the version number in the application's About dialog (Help > About Firefox/Thunderbird). If version is below the patched versions listed, the system is vulnerable.Check Version:
On Linux: firefox --version | head -1; On Windows: Check Help > About Firefox; On macOS: Check Firefox > About FirefoxVerify Fix Applied:
After updating, verify the version number matches or exceeds Firefox 83, Firefox ESR 78.5, or Thunderbird 78.5.📡 Detection & Monitoring
Log Indicators:
- Application crash logs with memory access violation errors
- Unexpected browser/email client termination events
- Process creation from browser processes with unusual command lines
Network Indicators:
- Unusual outbound connections from browser processes
- Traffic to known malicious domains or IPs
SIEM Query:
source="*firefox*" OR source="*thunderbird*" AND (event_type="crash" OR event_type="process_creation")🔗 References
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=1551615%2C1607762%2C1656697%2C1657739%2C1660236%2C1667912%2C1671479%2C1671923
- https://www.mozilla.org/security/advisories/mfsa2020-50/
- https://www.mozilla.org/security/advisories/mfsa2020-51/
- https://www.mozilla.org/security/advisories/mfsa2020-52/
- https://bugzilla.mozilla.org/buglist.cgi?bug_id=1551615%2C1607762%2C1656697%2C1657739%2C1660236%2C1667912%2C1671479%2C1671923
- https://www.mozilla.org/security/advisories/mfsa2020-50/
- https://www.mozilla.org/security/advisories/mfsa2020-51/
- https://www.mozilla.org/security/advisories/mfsa2020-52/
