CVE-2021-34595
📋 TL;DR
CVE-2021-34595 is an out-of-bounds read/write vulnerability in CODESYS V2 Runtime Toolkit and PLCWinNT software. Attackers can send crafted requests with invalid offsets to cause denial-of-service or local memory corruption. This affects industrial control systems using vulnerable versions of these CODESYS products.
💻 Affected Systems
- CODESYS V2 Runtime Toolkit 32 Bit full
- PLCWinNT
📦 What is this software?
Codesys by Codesys
Plcwinnt by Codesys
⚠️ Risk & Real-World Impact
Worst Case
Local memory overwrite could lead to arbitrary code execution, potentially compromising the PLC controller and allowing attackers to manipulate industrial processes.
Likely Case
Denial-of-service conditions disrupting PLC operations, causing industrial process interruptions or downtime.
If Mitigated
Limited impact if systems are isolated from untrusted networks and proper access controls are implemented.
🎯 Exploit Status
Exploitation requires crafting specific requests with invalid offsets. No public exploit code was found at time of analysis.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V2.4.7.56 or later
Vendor Advisory: https://customers.codesys.com/index.php?eID=dumpFile&t=f&f=16878&token=e5644ec405590e66aefa62304cb8632df9fc9e9c&download=
Restart Required: Yes
Instructions:
1. Download patch from CODESYS customer portal. 2. Backup current configuration. 3. Install update following vendor instructions. 4. Restart affected systems. 5. Verify version update.
🔧 Temporary Workarounds
Network Segmentation
allIsolate CODESYS systems from untrusted networks using firewalls and VLANs.
Access Control Restrictions
allImplement strict network access controls to limit who can communicate with CODESYS services.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate vulnerable systems
- Deploy intrusion detection systems to monitor for exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check CODESYS software version against affected versions list. Review system logs for abnormal requests or crashes.Check Version:
Check CODESYS Control application or runtime properties for version informationVerify Fix Applied:
Verify installed version is V2.4.7.56 or later using CODESYS version check utilities.📡 Detection & Monitoring
Log Indicators:
- Unexpected process crashes
- Memory access violation errors
- Abnormal network requests to CODESYS services
Network Indicators:
- Unusual traffic patterns to CODESYS ports (typically 1217, 2455)
SIEM Query:
source="CODESYS" AND (event_type="crash" OR error="memory" OR error="access")