CVE-2021-42020
📋 TL;DR
This vulnerability in Siemens RUGGEDCOM industrial networking devices allows attackers to exploit a TFTP functionality flaw where file names lack proper null termination checks. Exploitation could lead to data corruption or application crashes, affecting numerous RUGGEDCOM product lines used in critical infrastructure environments.
💻 Affected Systems
- RUGGEDCOM i800
- RUGGEDCOM i800NC
- RUGGEDCOM i801
- RUGGEDCOM i801NC
- RUGGEDCOM i802
- RUGGEDCOM i802NC
- RUGGEDCOM i803
- RUGGEDCOM i803NC
- RUGGEDCOM M2100
- RUGGEDCOM M2100NC
- RUGGEDCOM M2200
- RUGGEDCOM M2200NC
- RUGGEDCOM M969
- RUGGEDCOM M969NC
- RUGGEDCOM RMC30
- RUGGEDCOM RMC30NC
- RUGGEDCOM RMC8388 V4.X
- RUGGEDCOM RMC8388 V5.X
- RUGGEDCOM RMC8388NC V4.X
- RUGGEDCOM RMC8388NC V5.X
- RUGGEDCOM RP110
- RUGGEDCOM RP110NC
- RUGGEDCOM RS1600
- RUGGEDCOM RS1600F
- RUGGEDCOM RS1600FNC
- RUGGEDCOM RS1600NC
- RUGGEDCOM RS1600T
- RUGGEDCOM RS1600TNC
- RUGGEDCOM RS400
- RUGGEDCOM RS400NC
- RUGGEDCOM RS401
- RUGGEDCOM RS401NC
- RUGGEDCOM RS416
- RUGGEDCOM RS416NC
- RUGGEDCOM RS416NCv2 V4.X
- RUGGEDCOM RS416NCv2 V5.X
- RUGGEDCOM RS416P
- RUGGEDCOM RS416PNC
- RUGGEDCOM RS416PNCv2 V4.X
- RUGGEDCOM RS416PNCv2 V5.X
- RUGGEDCOM RS416Pv2 V4.X
- RUGGEDCOM RS416Pv2 V5.X
- RUGGEDCOM RS416v2 V4.X
- RUGGEDCOM RS416v2 V5.X
- RUGGEDCOM RS8000
- RUGGEDCOM RS8000A
- RUGGEDCOM RS8000ANC
- RUGGEDCOM RS8000H
- RUGGEDCOM RS8000HNC
- RUGGEDCOM RS8000NC
- RUGGEDCOM RS8000T
- RUGGEDCOM RS8000TNC
- RUGGEDCOM RS900
- RUGGEDCOM RS900 (32M) V4.X
- RUGGEDCOM RS900 (32M) V5.X
- RUGGEDCOM RS900G
- RUGGEDCOM RS900G (32M) V4.X
- RUGGEDCOM RS900G (32M) V5.X
- RUGGEDCOM RS900GNC
- RUGGEDCOM RS900GNC(32M) V4.X
- RUGGEDCOM RS900GNC(32M) V5.X
- RUGGEDCOM RS900GP
- RUGGEDCOM RS900GPNC
- RUGGEDCOM RS900L
- RUGGEDCOM RS900LNC
- RUGGEDCOM RS900M-GETS-C01
- RUGGEDCOM RS900M-GETS-XX
- RUGGEDCOM RS900M-STND-C01
- RUGGEDCOM RS900M-STND-XX
- RUGGEDCOM RS900MNC-GETS-C01
- RUGGEDCOM RS900MNC-GETS-XX
- RUGGEDCOM RS900MNC-STND-XX
- RUGGEDCOM RS900MNC-STND-XX-C01
- RUGGEDCOM RS900NC
- RUGGEDCOM RS900NC(32M) V4.X
- RUGGEDCOM RS900NC(32M) V5.X
- RUGGEDCOM RS900W
- RUGGEDCOM RS910
- RUGGEDCOM RS910L
- RUGGEDCOM RS910LNC
- RUGGEDCOM RS910NC
- RUGGEDCOM RS910W
- RUGGEDCOM RS920L
- RUGGEDCOM RS920LNC
- RUGGEDCOM RS920W
- RUGGEDCOM RS930L
- RUGGEDCOM RS930LNC
- RUGGEDCOM RS930W
- RUGGEDCOM RS940G
- RUGGEDCOM RS940GNC
- RUGGEDCOM RS969
- RUGGEDCOM RS969NC
- RUGGEDCOM RSG2100
- RUGGEDCOM RSG2100 (32M) V4.X
- RUGGEDCOM RSG2100 (32M) V5.X
- RUGGEDCOM RSG2100NC
- RUGGEDCOM RSG2100NC(32M) V4.X
- RUGGEDCOM RSG2100NC(32M) V5.X
- RUGGEDCOM RSG2100P
- RUGGEDCOM RSG2100P (32M) V4.X
- RUGGEDCOM RSG2100P (32M) V5.X
- RUGGEDCOM RSG2100PNC
- RUGGEDCOM RSG2100PNC (32M) V4.X
- RUGGEDCOM RSG2100PNC (32M) V5.X
- RUGGEDCOM RSG2200
- RUGGEDCOM RSG2200NC
- RUGGEDCOM RSG2288 V4.X
- RUGGEDCOM RSG2288 V5.X
- RUGGEDCOM RSG2288NC V4.X
- RUGGEDCOM RSG2288NC V5.X
- RUGGEDCOM RSG2300 V4.X
- RUGGEDCOM RSG2300 V5.X
- RUGGEDCOM RSG2300NC V4.X
- RUGGEDCOM RSG2300NC V5.X
- RUGGEDCOM RSG2300P V4.X
- RUGGEDCOM RSG2300P V5.X
- RUGGEDCOM RSG2300PNC V4.X
- RUGGEDCOM RSG2300PNC V5.X
- RUGGEDCOM RSG2488 V4.X
- RUGGEDCOM RSG2488 V5.X
- RUGGEDCOM RSG2488NC V4.X
- RUGGEDCOM RSG2488NC V5.X
- RUGGEDCOM RSG907R
- RUGGEDCOM RSG908C
- RUGGEDCOM RSG909R
- RUGGEDCOM RSG910C
- RUGGEDCOM RSG920P V4.X
- RUGGEDCOM RSG920P V5.X
- RUGGEDCOM RSG920PNC V4.X
- RUGGEDCOM RSG920PNC V5.X
- RUGGEDCOM RSL910
- RUGGEDCOM RSL910NC
- RUGGEDCOM RST2228
- RUGGEDCOM RST2228P
- RUGGEDCOM RST916C
- RUGGEDCOM RST916P
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device failure (hard-fault) leading to network disruption in industrial control systems, potentially causing operational downtime in critical infrastructure.
Likely Case
Data corruption and application crashes requiring device reboots, causing temporary service interruptions.
If Mitigated
Limited impact if TFTP is disabled or network access is restricted, with only minor service disruptions.
🎯 Exploit Status
Exploitation requires network access to TFTP service (UDP port 69). No authentication needed if TFTP is exposed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Siemens advisory for specific firmware updates
Vendor Advisory: https://cert-portal.siemens.com/productcert/html/ssa-256353.html
Restart Required: Yes
Instructions:
1. Review Siemens advisory SSA-256353. 2. Identify affected RUGGEDCOM devices. 3. Download appropriate firmware updates from Siemens support portal. 4. Apply updates following Siemens documentation. 5. Verify TFTP functionality after update.
🔧 Temporary Workarounds
Disable TFTP Service
allDisable TFTP functionality on affected devices if not required for operations.
Consult RUGGEDCOM device documentation for TFTP disable commands
Network Segmentation
allRestrict network access to TFTP service using firewall rules.
Configure firewall to block UDP port 69 from untrusted networks
🧯 If You Can't Patch
- Disable TFTP service immediately if not essential for operations
- Implement strict network segmentation to isolate RUGGEDCOM devices from untrusted networks
🔍 How to Verify
Check if Vulnerable:
Check if TFTP service is enabled on RUGGEDCOM devices using device management interface or network scanning tools.Check Version:
Use RUGGEDCOM CLI or web interface to check firmware version (specific commands vary by model)Verify Fix Applied:
Verify firmware version matches patched versions in Siemens advisory and test TFTP functionality.📡 Detection & Monitoring
Log Indicators:
- TFTP service crashes
- Unexpected device reboots
- TFTP error messages in system logs
Network Indicators:
- Unusual TFTP traffic patterns
- TFTP requests with malformed file names
SIEM Query:
Search for TFTP-related error events or device crash logs from RUGGEDCOM systems