CVE-2025-40593
📋 TL;DR
This vulnerability in Siemens SIMATIC CN 4100 allows attackers to store arbitrary files in the device's SFTP folder, potentially causing denial of service. All versions before V4.0 are affected. This impacts industrial control systems using these communication modules.
💻 Affected Systems
- Siemens SIMATIC CN 4100
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device unavailability disrupting industrial processes, potentially causing production downtime or safety issues in critical infrastructure.
Likely Case
Temporary service disruption requiring manual intervention to restore normal operation.
If Mitigated
Minimal impact with proper network segmentation and access controls limiting exposure.
🎯 Exploit Status
Requires SFTP access to the device. No authentication bypass mentioned in advisory.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V4.0
Vendor Advisory: https://cert-portal.siemens.com/productcert/html/ssa-626991.html
Restart Required: Yes
Instructions:
1. Download V4.0 firmware from Siemens support portal. 2. Backup current configuration. 3. Apply firmware update following Siemens documentation. 4. Verify successful update and restore configuration if needed.
🔧 Temporary Workarounds
Restrict SFTP Access
allLimit SFTP access to trusted IP addresses only using network controls.
Disable Unused SFTP Service
allIf SFTP functionality is not required, disable the service entirely.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate CN 4100 devices from untrusted networks.
- Monitor SFTP access logs for unauthorized file upload attempts and implement alerting.
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via Siemens TIA Portal or web interface. If version is below V4.0, device is vulnerable.Check Version:
Check via Siemens engineering software or device web interface - no universal CLI command available.Verify Fix Applied:
Confirm firmware version shows V4.0 or higher after update.📡 Detection & Monitoring
Log Indicators:
- Unusual SFTP file uploads
- Multiple failed SFTP authentication attempts
- Unexpected file creation in SFTP directories
Network Indicators:
- SFTP connections from unexpected source IPs
- Unusual SFTP traffic patterns
SIEM Query:
source="cn4100" AND (event="sftp_upload" OR event="file_create") AND NOT user IN ["authorized_users"]