CVE-2021-20861
📋 TL;DR
This vulnerability allows an authenticated attacker on the same network to bypass access controls and access the router's management interface. It affects multiple ELECOM LAN router models with specific firmware versions. Attackers can potentially gain administrative control over affected routers.
💻 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
Attacker gains full administrative access to router, enabling network traffic interception, DNS hijacking, credential theft, and deployment of persistent malware.
Likely Case
Attacker accesses management interface to change network settings, monitor traffic, or disable security features.
If Mitigated
With proper network segmentation and access controls, impact is limited to isolated network segments.
🎯 Exploit Status
Exploitation requires network adjacency and authenticated access, but specific vectors are unspecified in public disclosures.
🛠️ 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. Access router web interface. 2. Navigate to firmware update section. 3. Download latest firmware from ELECOM website. 4. Upload and apply firmware update. 5. Reboot router after update completes.
🔧 Temporary Workarounds
Network Segmentation
allIsolate router management interface to dedicated VLAN or separate network segment
Access Control Restrictions
allRestrict management interface access to specific trusted IP addresses only
🧯 If You Can't Patch
- Implement strict network segmentation to isolate router management traffic
- Monitor for unauthorized access attempts to router management interface
🔍 How to Verify
Check if Vulnerable:
Check router firmware version against affected versions list in vendor advisoryCheck Version:
Access router web interface and navigate to System Information or Status pageVerify Fix Applied:
Confirm firmware version is updated beyond vulnerable versions specified in advisory📡 Detection & Monitoring
Log Indicators:
- Unauthorized access attempts to management interface
- Unexpected configuration changes
Network Indicators:
- Unusual traffic patterns to router management ports
- Multiple authentication attempts from single source
SIEM Query:
source_ip=router_management_interface AND (status_code=200 OR status_code=302) AND user_agent NOT IN (trusted_user_agents)