CVE-2021-20863
📋 TL;DR
This CVE describes an OS command injection vulnerability in multiple ELECOM router models that allows authenticated attackers on the same network to execute arbitrary commands with root privileges. The vulnerability affects users of specific ELECOM router firmware versions who have not applied security updates. Attackers can gain complete control over affected routers.
💻 Affected Systems
- ELECOM 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 allowing attackers to intercept all network traffic, install persistent backdoors, pivot to internal networks, and use the router for further attacks.
Likely Case
Router takeover leading to network traffic interception, credential theft, DNS hijacking, and potential lateral movement to connected devices.
If Mitigated
Limited impact if proper network segmentation, strong authentication, and monitoring are in place, though router compromise still poses significant risk.
🎯 Exploit Status
Exploitation requires authenticated access but is likely straightforward once authentication is obtained. No public exploit code is available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor advisory for specific fixed versions per model
Vendor Advisory: https://www.elecom.co.jp/news/security/20211130-01/
Restart Required: Yes
Instructions:
1. Visit ELECOM support website. 2. Download latest firmware for your specific router model. 3. Log into router admin interface. 4. Navigate to firmware update section. 5. Upload and apply the new firmware. 6. Reboot router after update completes.
🔧 Temporary Workarounds
Network Segmentation
allIsolate router management interface to separate VLAN or network segment
Strong Authentication
allImplement complex passwords and consider multi-factor authentication if supported
🧯 If You Can't Patch
- Replace affected routers with updated models or different brands
- Implement strict network access controls to limit who can reach router management interfaces
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface and compare against affected versions listCheck Version:
Log into router admin interface and check firmware/version information pageVerify Fix Applied:
Verify firmware version has been updated to a version newer than those listed in affected versions📡 Detection & Monitoring
Log Indicators:
- Unusual authentication attempts to router admin interface
- Unexpected configuration changes
- Unusual command execution patterns in system logs
Network Indicators:
- Unusual outbound connections from router
- DNS configuration changes
- Unexpected traffic redirection
SIEM Query:
source="router_logs" AND (event_type="authentication" AND result="failure" AND count>10) OR (event_type="configuration_change" AND user!="admin")