CVE-2021-34413
📋 TL;DR
A Time-of-check Time-of-use (TOC/TOU) vulnerability in the Zoom Plugin for Microsoft Outlook on macOS allows standard users to write malicious applications to the plugin directory during installation. This could enable privilege escalation where malicious code executes with elevated privileges. Affects all macOS users running Zoom Plugin for Outlook versions before 5.3.52553.0918.
💻 Affected Systems
- Zoom Plugin for Microsoft Outlook
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker with local access could escalate privileges to root/admin level, install persistent backdoors, access sensitive system files, or compromise other user accounts on the same system.
Likely Case
Malicious local user or malware with standard privileges could gain administrative access to install additional malware, modify system configurations, or access protected data.
If Mitigated
With proper user privilege separation and application whitelisting, impact is limited to the user's own context without system-wide compromise.
🎯 Exploit Status
Requires local access and ability to write to plugin directory during installation. Exploitation involves race condition timing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 5.3.52553.0918 and later
Vendor Advisory: https://explore.zoom.us/en/trust/security/security-bulletin/
Restart Required: Yes
Instructions:
1. Open Microsoft Outlook on macOS. 2. Navigate to Zoom plugin settings. 3. Check for updates or manually update to version 5.3.52553.0918 or later. 4. Restart Outlook after update completes.
🔧 Temporary Workarounds
Uninstall Zoom Plugin
macosRemove the vulnerable Zoom Plugin from Microsoft Outlook
Open Microsoft Outlook > Go to Preferences > Extensions > Select Zoom Plugin > Click Remove
Restrict User Privileges
macosImplement least privilege by ensuring users don't have write access to system directories
sudo chmod -R 755 /Library/Application\ Support/zoom.us/
sudo chown root:wheel /Library/Application\ Support/zoom.us/
🧯 If You Can't Patch
- Remove the Zoom Plugin from Microsoft Outlook entirely
- Implement application whitelisting to prevent unauthorized executables from running
🔍 How to Verify
Check if Vulnerable:
Check Zoom Plugin version in Microsoft Outlook: Open Outlook > Preferences > Extensions > Zoom Plugin > Check version numberCheck Version:
grep -i version ~/Library/Application\ Support/zoom.us/plugin/outlook/*.plist 2>/dev/null || echo 'Plugin not found'Verify Fix Applied:
Verify version is 5.3.52553.0918 or higher in Outlook extensions settings📡 Detection & Monitoring
Log Indicators:
- Unusual file writes to /Library/Application Support/zoom.us/ during plugin installation
- Process execution from zoom plugin directory with elevated privileges
Network Indicators:
- Outbound connections from zoom plugin processes to unexpected destinations
SIEM Query:
process.name:zoom AND process.integrity_level:high AND file.path:/Library/Application Support/zoom.us/*