CVE-2021-34415
📋 TL;DR
This vulnerability in Zoom On-Premise Meeting Connector Controller allows attackers to crash the Zone Controller service by sending specially crafted network packets with manipulated cnt fields, causing resource exhaustion. It affects organizations running vulnerable versions of the Zoom On-Premise Meeting Connector Controller.
💻 Affected Systems
- Zoom On-Premise Meeting Connector Controller
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service for Zoom meetings hosted through the on-premise connector, disrupting business communications and collaboration.
Likely Case
Service disruption requiring manual restart of the Zone Controller service, causing temporary meeting interruptions.
If Mitigated
No impact if patched or if network controls prevent unauthorized access to the service.
🎯 Exploit Status
The vulnerability requires network access to the Zone Controller service but no authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 4.6.358.20210205 and later
Vendor Advisory: https://explore.zoom.us/en/trust/security/security-bulletin/
Restart Required: Yes
Instructions:
1. Download the patched version from Zoom's official portal. 2. Backup current configuration. 3. Install the update following Zoom's deployment guide. 4. Restart the Zone Controller service.
🔧 Temporary Workarounds
Network Segmentation
allRestrict network access to the Zone Controller service to only trusted management networks.
Rate Limiting
linuxImplement network-level rate limiting to prevent resource exhaustion attacks.
iptables -A INPUT -p tcp --dport [ZOOM_PORT] -m limit --limit 10/min --limit-burst 20 -j ACCEPT
iptables -A INPUT -p tcp --dport [ZOOM_PORT] -j DROP
🧯 If You Can't Patch
- Implement strict network access controls to limit which systems can communicate with the Zone Controller service.
- Monitor system resource usage and implement alerts for abnormal memory/CPU consumption on the Zoom controller.
🔍 How to Verify
Check if Vulnerable:
Check the Zoom On-Premise Meeting Connector Controller version in the admin interface or configuration files.Check Version:
Check Zoom controller admin interface or consult deployment documentation for version checking method.Verify Fix Applied:
Verify the version is 4.6.358.20210205 or later and test service functionality.📡 Detection & Monitoring
Log Indicators:
- Multiple connection attempts to Zone Controller service
- Service crash/restart events in system logs
- Abnormal memory consumption patterns
Network Indicators:
- High volume of small packets to Zoom controller port
- Unusual traffic patterns from untrusted sources
SIEM Query:
source="zoom-controller" AND (event="crash" OR event="restart" OR memory_usage>90)