CVE-2025-40939
📋 TL;DR
A vulnerability in SIMATIC CN 4100 devices allows attackers with physical access to trigger a denial-of-service reboot via the USB port. This affects all versions before V4.0.1 of Siemens' SIMATIC CN 4100 industrial communication device. The vulnerability requires physical access to exploit.
💻 Affected Systems
- Siemens SIMATIC CN 4100
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
An attacker with physical access could repeatedly reboot the device, causing sustained denial of service that disrupts industrial operations and communication networks.
Likely Case
Temporary disruption of network connectivity and industrial processes until the device reboots and recovers, potentially causing production delays.
If Mitigated
Minimal impact if physical access controls are properly implemented and monitored.
🎯 Exploit Status
Exploitation requires physical access to the USB port but no authentication or special tools. The vulnerability is documented in the Siemens advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V4.0.1
Vendor Advisory: https://cert-portal.siemens.com/productcert/html/ssa-416652.html
Restart Required: Yes
Instructions:
1. Download firmware V4.0.1 from Siemens support portal. 2. Backup current configuration. 3. Upload and install the new firmware via web interface or management tools. 4. Verify installation and restore configuration if needed.
🔧 Temporary Workarounds
Disable or secure USB port
allPhysically disable or secure the USB port to prevent unauthorized access
Implement physical security controls
allRestrict physical access to devices through locked cabinets, access controls, and surveillance
🧯 If You Can't Patch
- Implement strict physical access controls to prevent unauthorized personnel from reaching devices
- Monitor device logs for unexpected reboots and investigate physical access events
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or CLI. If version is below V4.0.1, device is vulnerable.Check Version:
Check via web interface at System > Device Information or via CLI command specific to Siemens devicesVerify Fix Applied:
Verify firmware version is V4.0.1 or higher after update. Test USB port functionality if required for operations.📡 Detection & Monitoring
Log Indicators:
- Unexpected device reboots
- USB connection events in system logs
- System crash or restart logs
Network Indicators:
- Sudden loss of connectivity from affected device
- Network topology changes due to device reboot
SIEM Query:
Device logs containing 'reboot', 'restart', 'crash', or 'USB' events from SIMATIC CN 4100 devices