CVE-2021-21891
📋 TL;DR
This vulnerability allows authenticated remote attackers to execute arbitrary code on Lantronix PremierWave 2050 devices by sending a specially crafted HTTP request that triggers a stack-based buffer overflow in the Web Manager's file deletion functionality. Affected systems are those running the vulnerable firmware version without proper network segmentation or access controls.
💻 Affected Systems
- Lantronix PremierWave 2050
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining root privileges, persistent backdoor installation, and complete control over the device and connected networks.
Likely Case
Remote code execution leading to device takeover, data exfiltration, and use as pivot point for lateral movement within the network.
If Mitigated
Limited impact if device is isolated, authentication is strong, and network monitoring detects anomalous HTTP requests.
🎯 Exploit Status
Exploit requires authentication but buffer overflow leads to reliable code execution. Detailed technical analysis available in Talos reports.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Lantronix security advisories for updated firmware
Vendor Advisory: https://www.lantronix.com/support/security-advisories/
Restart Required: Yes
Instructions:
1. Download latest firmware from Lantronix support portal. 2. Backup current configuration. 3. Upload firmware via web interface. 4. Apply update and reboot device.
🔧 Temporary Workarounds
Network Segmentation
allIsolate PremierWave devices in separate VLAN with strict firewall rules
Access Control
linuxRestrict web interface access to trusted IP addresses only
iptables -A INPUT -p tcp --dport 80 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
🧯 If You Can't Patch
- Disable web interface if not required and use alternative management methods
- Implement strict authentication policies and monitor for brute force attempts
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface: System > About, or SSH command: cat /etc/versionCheck Version:
cat /etc/version || grep 'Firmware' /var/www/html/index.htmlVerify Fix Applied:
Verify firmware version is updated beyond 8.9.0.0R4 and test file deletion functionality📡 Detection & Monitoring
Log Indicators:
- Multiple failed authentication attempts followed by successful login and file deletion requests
- Unusual HTTP POST requests to /FsBrowseClean endpoint with long parameters
Network Indicators:
- HTTP requests with abnormally long parameters to deletefile functionality
- Traffic from unexpected sources to device management interface
SIEM Query:
source="premierwave.log" AND ("FsBrowseClean" OR "deletefile") AND (content_length>1000 OR parameter_length>500)