CVE-2021-28152
📋 TL;DR
Hongdian H8922 devices have a backdoor telnet service on port 5188 with hardcoded superuser credentials (root:superzxmn). This allows attackers to gain complete control of affected devices. All Hongdian H8922 devices running firmware version 3.0.5 are vulnerable.
💻 Affected Systems
- Hongdian H8922
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise leading to network pivoting, data exfiltration, device bricking, or use in botnets/DDoS attacks.
Likely Case
Unauthorized administrative access allowing configuration changes, credential harvesting, and network reconnaissance.
If Mitigated
Limited impact if telnet is blocked at network perimeter and devices are isolated from untrusted networks.
🎯 Exploit Status
Exploitation requires only telnet client and knowledge of default credentials. No special tools or skills needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: http://en.hongdian.com/Products/Details/H8922
Restart Required: No
Instructions:
No official patch available. Contact Hongdian support for firmware updates or mitigation guidance.
🔧 Temporary Workarounds
Block Telnet Port
linuxBlock access to port 5188 using firewall rules to prevent exploitation.
iptables -A INPUT -p tcp --dport 5188 -j DROP
iptables -A OUTPUT -p tcp --dport 5188 -j DROP
Change Default Credentials
linuxChange root password if device management interface allows it.
passwd root
🧯 If You Can't Patch
- Isolate affected devices in separate VLAN with strict network segmentation
- Implement network monitoring for connections to port 5188
🔍 How to Verify
Check if Vulnerable:
Attempt telnet connection: telnet [device_ip] 5188, then login with root:superzxmnCheck Version:
Check device web interface or console for firmware versionVerify Fix Applied:
Verify telnet connection fails or credentials no longer work📡 Detection & Monitoring
Log Indicators:
- Failed/successful authentication attempts on port 5188
- Telnet service logs showing root login
Network Indicators:
- Outbound connections from device to suspicious IPs
- Unexpected telnet traffic on port 5188
SIEM Query:
source_port=5188 OR destination_port=5188 OR (protocol=telnet AND user=root)