CVE-2021-21879
📋 TL;DR
This vulnerability allows authenticated attackers to perform directory traversal attacks through the Web Manager File Upload functionality in Lantronix PremierWave 2050 devices. Attackers can overwrite arbitrary files on the system, potentially leading to complete system compromise. Only users running the affected firmware version are impacted.
💻 Affected Systems
- Lantronix PremierWave 2050
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system takeover through arbitrary file overwrite leading to remote code execution, device bricking, or persistent backdoor installation.
Likely Case
Unauthorized file modification leading to service disruption, configuration changes, or credential theft.
If Mitigated
Limited impact due to network segmentation, strong authentication controls, and file integrity monitoring.
🎯 Exploit Status
Exploitation requires valid credentials but uses simple directory traversal techniques.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 8.9.0.0R5 or later
Vendor Advisory: https://www.lantronix.com/support/software-updates/
Restart Required: Yes
Instructions:
1. Download latest firmware from Lantronix support portal. 2. Backup current configuration. 3. Upload firmware via Web Manager. 4. Apply update and restart device.
🔧 Temporary Workarounds
Disable Web Manager Access
linuxTemporarily disable Web Manager interface to prevent exploitation
# Disable web service via CLI
systemctl stop lantronix-webmanager
# Or block port via firewall
iptables -A INPUT -p tcp --dport 80 -j DROP
Restrict Network Access
linuxLimit Web Manager access to trusted IP addresses only
# Allow only specific IPs to access Web Manager
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Implement strict network segmentation to isolate PremierWave devices
- Enforce strong authentication policies and monitor for suspicious login attempts
🔍 How to Verify
Check if Vulnerable:
Check firmware version via Web Manager dashboard or CLI command: cat /etc/versionCheck Version:
cat /etc/versionVerify Fix Applied:
Verify firmware version is 8.9.0.0R5 or later and test file upload functionality with traversal attempts📡 Detection & Monitoring
Log Indicators:
- HTTP requests containing '../' sequences in file upload parameters
- Multiple failed authentication attempts followed by successful login and file upload
Network Indicators:
- HTTP POST requests to upload endpoints with path traversal payloads
- Unusual file modification timestamps
SIEM Query:
source="web_logs" AND (uri="*upload*" AND (payload="*../*" OR payload="*..\\*"))