CVE-2021-33719
📋 TL;DR
A critical buffer overflow vulnerability in Siemens SIPROTEC 5 relays allows attackers to send specially crafted packets to port 4443/tcp, potentially causing denial-of-service or remote code execution. Affected systems include SIPROTEC 5 relays with CPU variants CP050, CP100, and CP300 running versions below V8.80. This vulnerability is particularly dangerous as it affects industrial control system devices used in critical infrastructure.
💻 Affected Systems
- SIPROTEC 5 relays with CPU variants CP050
- SIPROTEC 5 relays with CPU variants CP100
- SIPROTEC 5 relays with CPU variants CP300
📦 What is this software?
Siprotec 5 With Cpu Variant Cp050 by Siemens
Siprotec 5 With Cpu Variant Cp100 by Siemens
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete device compromise, manipulation of protection relay settings, disruption of power grid operations, and potential physical damage to electrical equipment.
Likely Case
Denial-of-service causing relay malfunction, loss of protection functions, and disruption of power distribution operations requiring manual intervention.
If Mitigated
Limited impact if devices are behind firewalls with strict network segmentation and proper access controls, though risk remains if internal network is compromised.
🎯 Exploit Status
The vulnerability requires sending specially crafted packets to port 4443/tcp, which is accessible without authentication. Given the critical nature and CVSS 9.8 score, weaponization is likely but not publicly confirmed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V8.80 or later
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-847986.pdf
Restart Required: Yes
Instructions:
1. Download firmware version V8.80 or later from Siemens support portal. 2. Follow Siemens firmware update procedures for SIPROTEC 5 devices. 3. Apply firmware update to affected relays. 4. Verify successful update and functionality.
🔧 Temporary Workarounds
Network segmentation and firewall rules
allRestrict access to port 4443/tcp on affected devices using firewalls and network segmentation
Disable unnecessary services
allIf port 4443/tcp is not required for operations, disable the service or block the port
🧯 If You Can't Patch
- Implement strict network segmentation to isolate SIPROTEC 5 devices from untrusted networks
- Deploy intrusion detection systems to monitor for anomalous traffic to port 4443/tcp
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via DIGSI 5 engineering tool or device web interface. If version is below V8.80, device is vulnerable.Check Version:
Use DIGSI 5 engineering software to connect to device and check firmware version in device propertiesVerify Fix Applied:
Verify firmware version is V8.80 or later using DIGSI 5 or device interface. Test device functionality and monitor for stability.📡 Detection & Monitoring
Log Indicators:
- Unusual connection attempts to port 4443/tcp
- Device restart or crash logs
- Abnormal traffic patterns to relay devices
Network Indicators:
- Malformed packets sent to port 4443/tcp
- Unusual traffic volume to industrial control devices
- Connection attempts from unauthorized IP addresses
SIEM Query:
source_port:4443 AND (packet_size:>1500 OR protocol_anomaly:true)