CVE-2021-33737
📋 TL;DR
A denial-of-service vulnerability in Siemens SIMATIC CP industrial communication modules allows remote attackers to crash affected devices by sending specially crafted packets to TCP port 102. The vulnerability affects multiple SIMATIC CP product families, requiring a device restart to restore normal operations.
💻 Affected Systems
- SIMATIC CP 343-1
- SIMATIC CP 343-1 Advanced
- SIMATIC CP 343-1 ERPC
- SIMATIC CP 343-1 Lean
- SIMATIC CP 443-1
- SIMATIC CP 443-1 Advanced
- SIPLUS NET CP 443-1
- SIPLUS NET CP 443-1 Advanced
📦 What is this software?
Simatic Cp 343 1 Advanced Firmware by Siemens
View all CVEs affecting Simatic Cp 343 1 Advanced Firmware →
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service requiring physical restart of industrial control system components, potentially disrupting manufacturing or industrial processes.
Likely Case
Temporary disruption of network communications to affected CP modules until manual restart is performed.
If Mitigated
No impact if devices are properly segmented and protected from untrusted network traffic.
🎯 Exploit Status
Exploitation requires sending specially crafted packets to port 102/tcp. No authentication required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V3.3 for CP 443-1 variants; No patch available for CP 343-1 variants
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-549234.pdf
Restart Required: Yes
Instructions:
1. Download firmware update from Siemens Industry Online Support. 2. Follow Siemens firmware update procedures for affected CP modules. 3. Restart devices after update.
🔧 Temporary Workarounds
Network Segmentation
allRestrict access to port 102/tcp using firewall rules to only trusted systems.
Network Monitoring
allImplement network monitoring for anomalous traffic patterns on port 102.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate affected devices from untrusted networks.
- Deploy intrusion detection systems to monitor for exploitation attempts on port 102.
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via Siemens TIA Portal or STEP 7 software.Check Version:
Use Siemens TIA Portal or STEP 7 to read device information and firmware version.Verify Fix Applied:
Verify firmware version is V3.3 or higher for CP 443-1 variants. No fix available for CP 343-1 variants.📡 Detection & Monitoring
Log Indicators:
- Device restart logs
- Communication failure logs on port 102
Network Indicators:
- Anomalous traffic patterns to port 102/tcp
- Multiple connection attempts to port 102
SIEM Query:
source_port:102 AND (packet_size:anomalous OR connection_rate:high)