CVE-2021-37317
📋 TL;DR
This CVE describes a directory traversal vulnerability in ASUS RT-AC68U router's Cloud Disk feature that allows remote attackers to write arbitrary files via improper input sanitization in COPY and MOVE operations. Attackers can potentially achieve remote code execution by writing malicious files to sensitive locations. Users of affected ASUS router firmware versions are vulnerable.
💻 Affected Systems
- ASUS RT-AC68U router
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to complete router compromise, credential theft, network traffic interception, and lateral movement into connected devices.
Likely Case
File system manipulation allowing attackers to modify configuration files, install backdoors, or disrupt router functionality.
If Mitigated
Limited impact if Cloud Disk feature is disabled or network access is restricted, though other attack vectors may still exist.
🎯 Exploit Status
Exploitation requires network access to the router's web interface or Cloud Disk service. Authentication status depends on specific configuration.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.0.0.4.386.41634 and later
Vendor Advisory: https://www.asus.com/support/FAQ/1046354/
Restart Required: Yes
Instructions:
1. Log into router web interface. 2. Navigate to Administration > Firmware Upgrade. 3. Check for updates or manually upload firmware version 3.0.0.4.386.41634 or later. 4. Apply update and wait for router to reboot.
🔧 Temporary Workarounds
Disable Cloud Disk
allTurn off the vulnerable Cloud Disk feature to prevent exploitation
Navigate to USB Application > Cloud Disk in router web interface and disable
Restrict Network Access
allLimit access to router administration interface
Configure firewall rules to restrict access to router IP on ports 80/443
🧯 If You Can't Patch
- Disable Cloud Disk feature immediately
- Implement network segmentation to isolate router from critical systems
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router web interface under Administration > Firmware UpgradeCheck Version:
Check router web interface or use: curl -s http://router-ip/Advanced_FirmwareUpgrade_Content.asp | grep firmware_versionVerify Fix Applied:
Confirm firmware version is 3.0.0.4.386.41634 or later📡 Detection & Monitoring
Log Indicators:
- Unusual file operations in Cloud Disk logs
- Multiple failed COPY/MOVE operations with path traversal patterns
Network Indicators:
- HTTP requests to Cloud Disk endpoints with ../ sequences in parameters
- Unusual traffic to router administration interface
SIEM Query:
source="router_logs" AND ("Cloud Disk" OR "COPY" OR "MOVE") AND ("..\/" OR "%2e%2e%2f")