CVE-2021-21869
📋 TL;DR
This CVE describes an unsafe deserialization vulnerability in CODESYS Development System that allows arbitrary command execution when processing malicious files. Attackers can exploit this by providing specially crafted files to vulnerable systems. Affected users include anyone using CODESYS Development System 3.5.16 or 3.5.17 for industrial control system development.
💻 Affected Systems
- CODESYS GmbH CODESYS Development System
📦 What is this software?
Codesys by Codesys
Codesys by Codesys
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with remote code execution leading to industrial process disruption, data theft, or ransomware deployment.
Likely Case
Local privilege escalation leading to unauthorized access to engineering workstations and potential lateral movement within industrial networks.
If Mitigated
Limited impact with proper network segmentation and file validation controls preventing malicious file execution.
🎯 Exploit Status
Exploitation requires user interaction to open malicious files. TALOS-2021-1306 provides technical details.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.5.18.0 or later
Vendor Advisory: https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16805&token=ee583c498941d9fda86490bca98ff21928eec08a&download=
Restart Required: Yes
Instructions:
1. Download CODESYS Development System 3.5.18.0 or later from official vendor site. 2. Backup existing projects. 3. Install the update following vendor instructions. 4. Restart affected systems.
🔧 Temporary Workarounds
Restrict file processing
allImplement strict file validation and only allow trusted files to be processed by CODESYS Development System.
User awareness training
allTrain users to only open files from trusted sources and verify file integrity before processing.
🧯 If You Can't Patch
- Implement network segmentation to isolate CODESYS development systems from critical production networks
- Deploy application whitelisting to prevent execution of unauthorized processes
🔍 How to Verify
Check if Vulnerable:
Check CODESYS Development System version in Help > About menu. If version is 3.5.16 or 3.5.17, system is vulnerable.Check Version:
In CODESYS Development System: Help > About menu displays version informationVerify Fix Applied:
Verify version is 3.5.18.0 or later in Help > About menu and test file processing functionality.📡 Detection & Monitoring
Log Indicators:
- Unusual file processing events
- Unexpected process execution from CODESYS
- Error logs related to Engine.plugin ProfileInformation
Network Indicators:
- Unexpected outbound connections from CODESYS systems
- File transfers to/from development workstations
SIEM Query:
source="CODESYS" AND (event_type="file_processing" OR process_name="Engine.plugin")🔗 References
- https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16805&token=ee583c498941d9fda86490bca98ff21928eec08a&download=
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1306
- https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16805&token=ee583c498941d9fda86490bca98ff21928eec08a&download=
- https://talosintelligence.com/vulnerability_reports/TALOS-2021-1306
