CVE-2021-41769
📋 TL;DR
An improper input validation vulnerability in the web server of Siemens SIPROTEC 5 devices allows unauthenticated attackers to access device information. This affects multiple SIPROTEC 5 models with CPU variants CP300, CP100, and CP050 running firmware versions below V8.83, used in industrial control systems for protection and automation.
💻 Affected Systems
- SIPROTEC 5 6MD85
- SIPROTEC 5 6MD86
- SIPROTEC 5 6MD89
- SIPROTEC 5 6MU85
- SIPROTEC 5 7KE85
- SIPROTEC 5 7SA82
- SIPROTEC 5 7SA86
- SIPROTEC 5 7SA87
- SIPROTEC 5 7SD82
- SIPROTEC 5 7SD86
- SIPROTEC 5 7SD87
- SIPROTEC 5 7SJ81
- SIPROTEC 5 7SJ82
- SIPROTEC 5 7SJ85
- SIPROTEC 5 7SJ86
- SIPROTEC 5 7SK82
- SIPROTEC 5 7SK85
- SIPROTEC 5 7SL82
- SIPROTEC 5 7SL86
- SIPROTEC 5 7SL87
- SIPROTEC 5 7SS85
- SIPROTEC 5 7ST85
- SIPROTEC 5 7SX85
- SIPROTEC 5 7UM85
- SIPROTEC 5 7UT82
- SIPROTEC 5 7UT85
- SIPROTEC 5 7UT86
- SIPROTEC 5 7UT87
- SIPROTEC 5 7VE85
- SIPROTEC 5 7VK87
- SIPROTEC 5 Compact 7SX800
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Exploitation could lead to unauthorized access to sensitive device information, potentially enabling reconnaissance for further attacks, disruption of critical infrastructure operations, or manipulation of protection settings in worst-case scenarios.
Likely Case
Most probable impact is information disclosure, where attackers gather device details to plan targeted attacks or assess network vulnerabilities without authentication.
If Mitigated
With proper network segmentation and access controls, impact is limited to isolated network segments, reducing exposure and preventing broader system compromise.
🎯 Exploit Status
Exploitation likely involves sending crafted requests to the web server; no public proof-of-concept is known, but low complexity suggests it may be easily replicable.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V8.83 or later
Vendor Advisory: https://cert-portal.siemens.com/productcert/pdf/ssa-439673.pdf
Restart Required: Yes
Instructions:
1. Download firmware version V8.83 or later from Siemens support portal. 2. Follow Siemens instructions for firmware update on affected SIPROTEC 5 devices. 3. Restart the device after update to apply changes.
🔧 Temporary Workarounds
Restrict network access
allLimit access to the web server by blocking unnecessary inbound traffic using firewalls or network segmentation.
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
Disable web server if not needed
allTurn off the web server functionality on devices where it is not required for operations.
Refer to Siemens device configuration manual for web server disable steps
🧯 If You Can't Patch
- Implement strict network segmentation to isolate affected devices from untrusted networks.
- Monitor network traffic for unusual access attempts to device web interfaces and review logs regularly.
🔍 How to Verify
Check if Vulnerable:
Check the firmware version on the device via its web interface or management console; if version is below V8.83, it is vulnerable.Check Version:
Use Siemens DIGSI 5 software or device web interface to view firmware version; no universal command as it varies by device model.Verify Fix Applied:
After updating, confirm the firmware version is V8.83 or higher using the same method.📡 Detection & Monitoring
Log Indicators:
- Unauthenticated access attempts to web server endpoints
- Unusual HTTP requests to device information pages
Network Indicators:
- Traffic to device web ports (e.g., 80, 443) from unauthorized sources
- Spikes in requests to specific URIs related to device data
SIEM Query:
source="device_logs" AND (event="unauthorized_access" OR uri="/device_info")