CVE-2021-20859
📋 TL;DR
This vulnerability allows an authenticated attacker on the same network to execute arbitrary operating system commands on affected ELECOM LAN routers. Attackers can gain full control of the router, potentially compromising the entire network. Users of specific ELECOM router models with vulnerable firmware versions are affected.
💻 Affected Systems
- WRC-1167GST2
- WRC-1167GST2A
- WRC-1167GST2H
- WRC-2533GS2-B
- WRC-2533GS2-W
- WRC-1750GS
- WRC-1750GSV
- WRC-1900GST
- WRC-2533GST
- WRC-2533GSTA
- WRC-2533GST2
- WRC-2533GST2SP
- WRC-2533GST2-G
- EDWRC-2533GST2
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router compromise leading to network takeover, data interception, malware deployment, and lateral movement to connected devices.
Likely Case
Router configuration modification, network traffic monitoring, credential theft, and potential pivot to internal systems.
If Mitigated
Limited to authenticated attackers on the local network, with proper segmentation reducing lateral movement opportunities.
🎯 Exploit Status
Exploitation requires authenticated access but unspecified vectors suggest multiple potential attack paths. CVSS 8.0 indicates high severity with low attack complexity.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Versions above those listed in affected versions (check specific model for exact patched version)
Vendor Advisory: https://www.elecom.co.jp/news/security/20211130-01/
Restart Required: Yes
Instructions:
1. Identify your router model and current firmware version. 2. Visit ELECOM support website for your region. 3. Download latest firmware for your specific model. 4. Access router admin interface. 5. Navigate to firmware update section. 6. Upload and apply new firmware. 7. Reboot router after update completes.
🔧 Temporary Workarounds
Network Segmentation
allIsolate router management interface to separate VLAN or network segment
Access Restriction
allRestrict router admin access to specific trusted IP addresses only
🧯 If You Can't Patch
- Replace affected routers with non-vulnerable models
- Implement strict network monitoring for suspicious router access patterns
🔍 How to Verify
Check if Vulnerable:
Check router admin interface for model and firmware version, compare against affected versions listCheck Version:
Access router web interface and check System Information or Firmware Status pageVerify Fix Applied:
Confirm firmware version is higher than affected versions listed in advisory📡 Detection & Monitoring
Log Indicators:
- Unusual authentication attempts to router admin interface
- Unexpected configuration changes
- Suspicious command execution in router logs
Network Indicators:
- Unusual traffic patterns from router to internal systems
- Router communicating with unexpected external IPs
SIEM Query:
Search for authentication events to router admin interface from non-standard IPs followed by configuration changes