CVE-2021-31337
📋 TL;DR
This vulnerability allows remote attackers to gain unauthorized access to SIMATIC HMI Comfort Panels and SINAMICS Medium Voltage Products via unauthenticated Telnet service. The Telnet service does not require authentication, enabling attackers to execute commands on affected devices. This affects industrial control systems in manufacturing, energy, and critical infrastructure sectors.
💻 Affected Systems
- SIMATIC HMI Comfort Panels
- SINAMICS SL150
- SINAMICS SM150
- SINAMICS SM150i
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of industrial control systems leading to production shutdown, equipment damage, safety system manipulation, or data exfiltration from critical infrastructure.
Likely Case
Unauthorized access to HMI panels allowing configuration changes, data theft, or disruption of industrial processes.
If Mitigated
Limited impact if Telnet is disabled and network segmentation prevents access to vulnerable services.
🎯 Exploit Status
Exploitation requires only Telnet client and network access to vulnerable service. No authentication bypass needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: N/A
Vendor Advisory: https://us-cert.cisa.gov/ics/advisories/icsa-21-131-04
Restart Required: No
Instructions:
1. Disable Telnet service on all affected devices. 2. Use Siemens SIMATIC STEP 7 or TIA Portal to configure devices. 3. Apply network segmentation to isolate affected systems.
🔧 Temporary Workarounds
Disable Telnet Service
allTurn off Telnet service on all affected devices to prevent unauthenticated access.
Configure via Siemens SIMATIC STEP 7 or TIA Portal interface
Network Segmentation
allIsolate affected devices in separate network segments with strict firewall rules.
Configure firewall to block Telnet port 23/tcp
🧯 If You Can't Patch
- Implement strict network access controls to block Telnet traffic (port 23/tcp) from untrusted networks
- Deploy network monitoring and intrusion detection for Telnet connection attempts
🔍 How to Verify
Check if Vulnerable:
Attempt Telnet connection to device port 23. If connection succeeds without authentication prompt, device is vulnerable.Check Version:
Check device firmware version via Siemens SIMATIC STEP 7 or TIA PortalVerify Fix Applied:
Verify Telnet service is disabled by attempting connection to port 23 and confirming connection refused.📡 Detection & Monitoring
Log Indicators:
- Successful Telnet connections without authentication
- Failed authentication attempts if authentication was enabled
Network Indicators:
- Telnet traffic (port 23/tcp) to industrial control systems
- Unusual Telnet connections from external IPs
SIEM Query:
source_port=23 OR destination_port=23 AND (device_type="industrial" OR device_vendor="Siemens")