CVE-2021-42887
📋 TL;DR
This vulnerability allows unauthenticated attackers to bypass the login mechanism on TOTOLINK EX1200T routers by sending a specially crafted request to formLoginAuth.htm. Affected users are those running vulnerable firmware versions on these specific router models, potentially exposing administrative access to unauthorized parties.
💻 Affected Systems
- TOTOLINK EX1200T
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of router with administrative access, enabling network traffic interception, DNS hijacking, malware deployment, and lateral movement into connected networks.
Likely Case
Unauthorized administrative access to router configuration, allowing network settings modification, credential harvesting, and potential denial of service.
If Mitigated
Limited impact if router is behind firewall with restricted WAN access, though internal attackers could still exploit.
🎯 Exploit Status
Simple HTTP request bypass with publicly available proof-of-concept; trivial to automate.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Unknown
Restart Required: No
Instructions:
Check vendor website for firmware updates; if unavailable, consider replacing hardware or implementing strict network controls.
🔧 Temporary Workarounds
Network Segmentation
allIsolate vulnerable router from critical networks using VLANs or separate physical network.
Access Control Lists
linuxRestrict access to router management interface to trusted IP addresses only.
iptables -A INPUT -p tcp --dport 80 -s TRUSTED_IP -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Disable remote management and only allow local network access to admin interface
- Monitor for suspicious authentication attempts and unexpected configuration changes
🔍 How to Verify
Check if Vulnerable:
Attempt to access formLoginAuth.htm with crafted payload; check router web interface for version information.Check Version:
Check router web interface under System Status or Administration settingsVerify Fix Applied:
Test login bypass with same payload after firmware update; verify authentication now required.📡 Detection & Monitoring
Log Indicators:
- Unusual access to formLoginAuth.htm
- Successful logins from unexpected IP addresses
- Configuration changes without proper authentication
Network Indicators:
- HTTP POST requests to formLoginAuth.htm with specific parameters
- Unauthenticated access to admin pages
SIEM Query:
source="router_logs" AND (uri="/formLoginAuth.htm" OR event="configuration_change")