CVE-2021-20988
📋 TL;DR
This vulnerability in Hilscher rcX RTOS allows attackers to send malformed UDP packets where the actual packet length doesn't match the length indicated in the packet header. This can cause a denial of service on affected devices. Systems using Hilscher rcX RTOS versions before V2.1.14.1 are affected.
💻 Affected Systems
- Hilscher rcX RTOS
📦 What is this software?
Ice1 16dio G60l C1 V1d Firmware by Pepperl Fuchs
Ice1 16dio G60l V1d Firmware by Pepperl Fuchs
Ice1 8di8do G60l C1 V1d Firmware by Pepperl Fuchs
Ice1 8di8do G60l V1d Firmware by Pepperl Fuchs
Ice1 8iol S2 G60l V1d Firmware by Pepperl Fuchs
Rcx Rtos by Hilscher
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service rendering the industrial device unavailable, potentially disrupting industrial processes or critical infrastructure operations.
Likely Case
Device crashes or becomes unresponsive requiring manual restart, causing temporary service disruption.
If Mitigated
Minimal impact with proper network segmentation and monitoring in place to detect and block malformed UDP packets.
🎯 Exploit Status
Exploitation requires network access to UDP ports on affected devices but no authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: V2.1.14.1 and later
Vendor Advisory: https://kb.hilscher.com/display/ISMS/2019-04-10+Wrong+handling+of+the+UDP+checksum
Restart Required: Yes
Instructions:
1. Download V2.1.14.1 or later from Hilscher support portal. 2. Backup current configuration. 3. Apply firmware update following vendor instructions. 4. Restart device. 5. Verify version update.
🔧 Temporary Workarounds
Network Segmentation
allIsolate affected devices in separate network segments with strict firewall rules.
UDP Port Filtering
allBlock unnecessary UDP traffic to affected devices at network perimeter.
🧯 If You Can't Patch
- Implement strict network access controls to limit UDP traffic to trusted sources only.
- Deploy network monitoring to detect and alert on malformed UDP packets targeting affected devices.
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via Hilscher configuration tools or web interface.Check Version:
Use Hilscher netX Studio or device web interface to check firmware version.Verify Fix Applied:
Confirm firmware version is V2.1.14.1 or later and test UDP communication functionality.📡 Detection & Monitoring
Log Indicators:
- Device crash logs
- UDP protocol violation alerts
- Unexpected device restarts
Network Indicators:
- Malformed UDP packets with mismatched length fields
- UDP flood to specific ports
SIEM Query:
udp AND (packet_length_mismatch OR protocol_violation) AND dest_ip:[affected_device_ips]