CVE-2020-20813
📋 TL;DR
This vulnerability in OpenVPN allows remote attackers to send crafted reset packets through the control channel, causing a denial of service (DoS) condition. It affects OpenVPN servers and clients running vulnerable versions, potentially disrupting VPN connectivity.
💻 Affected Systems
- OpenVPN
📦 What is this software?
Openvpn by Openvpn
⚠️ Risk & Real-World Impact
Worst Case
Complete VPN service disruption, preventing all encrypted communication through affected OpenVPN instances.
Likely Case
Temporary service interruption requiring OpenVPN process restart, causing connectivity loss for VPN users.
If Mitigated
Minimal impact with proper network segmentation and monitoring allowing quick detection and recovery.
🎯 Exploit Status
Crafted packet attack requires no authentication and is simple to execute.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: OpenVPN 2.4.8 and later
Vendor Advisory: https://openvpn.net/security-advisory/
Restart Required: Yes
Instructions:
1. Download OpenVPN 2.4.8 or later from openvpn.net. 2. Stop OpenVPN service. 3. Install updated version. 4. Restart OpenVPN service.
🔧 Temporary Workarounds
Network Filtering
linuxBlock or rate-limit control channel traffic from untrusted sources using firewall rules.
iptables -A INPUT -p tcp --dport 1194 -m state --state NEW -m recent --set
iptables -A INPUT -p tcp --dport 1194 -m state --state NEW -m recent --update --seconds 60 --hitcount 10 -j DROP
🧯 If You Can't Patch
- Implement network segmentation to isolate OpenVPN servers from untrusted networks
- Deploy intrusion detection systems to monitor for DoS attack patterns
🔍 How to Verify
Check if Vulnerable:
Check OpenVPN version with 'openvpn --version' and verify it's 2.4.7 or earlier.Check Version:
openvpn --version | head -1Verify Fix Applied:
Confirm version is 2.4.8 or later with 'openvpn --version' and test VPN connectivity.📡 Detection & Monitoring
Log Indicators:
- Multiple connection resets
- Unexpected control channel termination
- OpenVPN process crashes
Network Indicators:
- Unusual spike in control channel packets
- Malformed reset packets to OpenVPN port
SIEM Query:
source="openvpn.log" AND ("reset" OR "crash" OR "terminated")