CVE-2021-43083
📋 TL;DR
This vulnerability in Apache PLC4X's C implementation (PLC4C) allows unsigned integer underflow in the TCP transport layer. Attackers could exploit this by tricking users into connecting to malicious industrial devices that send specially crafted responses. Only users of the PLC4C library who connect to untrusted devices are affected.
💻 Affected Systems
- Apache PLC4X PLC4C (C language implementation)
📦 What is this software?
Plc4x by Apache
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete system compromise, data theft, or disruption of industrial control systems.
Likely Case
Denial of service causing application crashes or instability in PLC communication systems.
If Mitigated
No impact if systems only connect to trusted devices and have proper network segmentation.
🎯 Exploit Status
Exploitation requires the victim to actively connect to a malicious device. No public exploits known as of advisory date.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 0.9.1
Vendor Advisory: https://lists.apache.org/thread/jxx6qc84z60xbbhn6vp2s5qf09psrtc7
Restart Required: Yes
Instructions:
1. Download PLC4X version 0.9.1 or later from Apache repository. 2. Replace existing PLC4C library files with new version. 3. Recompile any applications using PLC4C. 4. Restart affected services.
🔧 Temporary Workarounds
Network Segmentation
allRestrict PLC4C applications to only connect to trusted, known-good industrial devices.
Firewall Rules
allImplement strict firewall rules to prevent connections to unknown or untrusted devices.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate PLC4C systems from untrusted networks
- Deploy intrusion detection systems to monitor for unusual PLC communication patterns
🔍 How to Verify
Check if Vulnerable:
Check PLC4C library version - if below 0.9.1, system is vulnerable.Check Version:
Check build configuration or library metadata for PLC4C version informationVerify Fix Applied:
Verify PLC4C version is 0.9.1 or higher after update.📡 Detection & Monitoring
Log Indicators:
- Application crashes in PLC4C processes
- Unexpected TCP connection resets from industrial devices
Network Indicators:
- Unusual TCP packet sizes or malformed responses from industrial devices
- Connections to unknown IP addresses on industrial ports
SIEM Query:
source="plc4c" AND (event_type="crash" OR event_type="error")