CVE-2021-47816
📋 TL;DR
Thecus N4800Eco NAS Server Control Panel contains a command injection vulnerability that allows authenticated attackers to execute arbitrary system commands through user management endpoints. Attackers can inject commands via username and batch user creation parameters to execute shell commands with administrative privileges. This affects organizations using Thecus N4800Eco NAS devices with the vulnerable control panel.
💻 Affected Systems
- Thecus N4800Eco NAS Server
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise allowing attackers to install persistent backdoors, exfiltrate all stored data, pivot to other network systems, or render the NAS inoperable.
Likely Case
Data theft, ransomware deployment, or unauthorized access to sensitive files stored on the NAS.
If Mitigated
Limited impact if proper network segmentation, strong authentication, and command input validation are implemented.
🎯 Exploit Status
Exploit code is publicly available on Exploit-DB (ID 49926). Attack requires valid credentials but command injection is straightforward once authenticated.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown specific version - check vendor for latest firmware
Vendor Advisory: http://www.thecus.com/
Restart Required: Yes
Instructions:
1. Log into Thecus web interface. 2. Navigate to System Management > Firmware Update. 3. Check for and apply latest firmware. 4. Reboot the NAS after update completes.
🔧 Temporary Workarounds
Disable Remote Access
linuxBlock external access to the NAS control panel to prevent exploitation from internet sources.
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
Restrict User Management
allLimit user management permissions to only essential administrators and implement strong password policies.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate the NAS from critical systems
- Enable detailed logging and monitor for suspicious user management activities
🔍 How to Verify
Check if Vulnerable:
Check firmware version against latest available from Thecus. If running outdated firmware, assume vulnerable.Check Version:
Check System Information in Thecus web interface or SSH to device and run: cat /etc/versionVerify Fix Applied:
Verify firmware has been updated to latest version and test user management functionality for command injection attempts.📡 Detection & Monitoring
Log Indicators:
- Unusual user creation/modification events
- Shell command execution from web interface logs
- Multiple failed authentication attempts followed by successful login
Network Indicators:
- Unexpected outbound connections from NAS
- Traffic to known malicious IPs
- Unusual patterns in web interface access
SIEM Query:
source="thecus_nas" AND (event="user_created" OR event="user_modified") AND command="*;*" OR command="*|*" OR command="*`*"