CVE-2025-40940
📋 TL;DR
A vulnerability in SIMATIC CN 4100 industrial communication devices allows attackers to exploit inconsistent SNMP behavior to access sensitive data, potentially breaching confidentiality. This affects all versions before V4.0.1 of Siemens SIMATIC CN 4100 devices used in industrial control systems.
💻 Affected Systems
- Siemens SIMATIC CN 4100
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could extract sensitive configuration data, network information, or operational parameters from industrial control systems, potentially enabling further attacks on critical infrastructure.
Likely Case
Unauthorized access to SNMP data revealing device configurations, network topology, or system status information that could be used for reconnaissance or targeted attacks.
If Mitigated
Limited exposure with proper network segmentation and access controls, restricting impact to isolated network segments.
🎯 Exploit Status
Exploitation requires network access to SNMP service. No authentication bypass needed if SNMP is enabled with default community strings.
🛠️ 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 new firmware via web interface or TIA Portal. 4. Restart device. 5. Verify firmware version.
🔧 Temporary Workarounds
Disable SNMP service
allTurn off SNMP protocol if not required for monitoring
Restrict SNMP access
allConfigure firewall rules to limit SNMP access to trusted management stations only
🧯 If You Can't Patch
- Implement strict network segmentation to isolate CN 4100 devices from untrusted networks
- Change SNMP community strings from defaults and implement SNMPv3 with authentication
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface (System Information) or TIA Portal. If version is below V4.0.1, device is vulnerable.Check Version:
snmpget -v2c -c public <device_ip> 1.3.6.1.2.1.1.1.0 (check system description for version)Verify Fix Applied:
Confirm firmware version shows V4.0.1 or higher in System Information. Test SNMP queries return consistent responses.📡 Detection & Monitoring
Log Indicators:
- Unusual SNMP query patterns
- Multiple failed SNMP requests from single source
- SNMP traffic from unexpected network segments
Network Indicators:
- SNMP traffic to CN 4100 devices from unauthorized IPs
- Abnormal SNMP response patterns
- UDP/161 traffic spikes
SIEM Query:
source_port=161 AND (dest_ip IN [CN4100_IPs]) AND (src_ip NOT IN [authorized_management_IPs])