CVE-2021-21730
📋 TL;DR
This vulnerability allows attackers to bypass authentication on ZTE ZXHN H168N routers via brute force attacks against the command-line interface (CLI). Attackers could gain administrative access to affected devices. This affects ZTE ZXHN H168N routers running version V3.5.0_TY.T6.
💻 Affected Systems
- ZTE ZXHN H168N
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of router with ability to modify configurations, intercept traffic, deploy malware, or use as pivot point into internal networks.
Likely Case
Unauthorized administrative access allowing network configuration changes, traffic monitoring, and credential harvesting.
If Mitigated
Limited impact if strong authentication controls, network segmentation, and monitoring are in place.
🎯 Exploit Status
Brute force attacks are well-understood and tools exist for automating CLI authentication attempts.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check ZTE support for updated firmware
Vendor Advisory: https://support.zte.com.cn/support/news/LoopholeInfoDetail.aspx?newsId=1014864
Restart Required: Yes
Instructions:
1. Check ZTE support site for firmware updates. 2. Download appropriate firmware for ZXHN H168N. 3. Backup current configuration. 4. Upload and apply firmware update via web interface. 5. Verify update applied successfully.
🔧 Temporary Workarounds
Disable Remote CLI Access
allDisable CLI access from external networks if not required
Implement Strong Authentication
allEnforce complex passwords and account lockout policies
🧯 If You Can't Patch
- Isolate router management interface to trusted internal networks only
- Implement network monitoring for brute force attempts against router
🔍 How to Verify
Check if Vulnerable:
Check router firmware version via web interface: System > Device Information > Software VersionCheck Version:
Check via router web interface or SSH if availableVerify Fix Applied:
Verify firmware version has been updated from V3.5.0_TY.T6📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts to CLI
- Successful CLI logins from unusual IPs
Network Indicators:
- Brute force traffic patterns to router management ports
- Unexpected configuration changes
SIEM Query:
source="router" AND (event="authentication failed" OR event="login") | stats count by src_ip dest_ip | where count > 10