CVE-2020-29656
📋 TL;DR
This vulnerability in RT-AC88U Download Master allows attackers to access unknown functionality through a direct web request to a specific CGI endpoint. It affects users of ASUS RT-AC88U routers running Download Master before version 3.1.0.108. The vulnerability enables information disclosure through what appears to be an authentication bypass or improper access control issue.
💻 Affected Systems
- ASUS RT-AC88U Download Master
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could gain unauthorized access to sensitive router configuration data, user credentials, or potentially execute arbitrary code through the exposed functionality.
Likely Case
Information disclosure of router settings, user data, or system information that could be used for further attacks.
If Mitigated
Limited impact if proper network segmentation and access controls prevent external access to the router's web interface.
🎯 Exploit Status
The vulnerability description mentions 'known to be easy' exploitation via unspecified public exploit, suggesting low technical barriers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.1.0.108 or later
Vendor Advisory: https://www.asus.com/support/FAQ/1048284/
Restart Required: Yes
Instructions:
1. Log into router web interface
2. Navigate to Administration > Firmware Upgrade
3. Check for updates and install latest firmware
4. After update, navigate to USB Application > Download Master
5. Ensure Download Master version is 3.1.0.108 or higher
6. Reboot router
🔧 Temporary Workarounds
Disable Download Master
allTemporarily disable the vulnerable component until patching is possible
Navigate to USB Application > Download Master in router web interface and toggle to OFF
Restrict Web Interface Access
allLimit access to router web interface to trusted internal IPs only
In router web interface: Administration > System > Enable 'Access Restriction' and specify allowed IP ranges
🧯 If You Can't Patch
- Disable Download Master feature completely
- Implement strict firewall rules to block external access to router web interface (ports 80/443)
🔍 How to Verify
Check if Vulnerable:
Access router web interface, navigate to USB Application > Download Master, check version number. If version is below 3.1.0.108, system is vulnerable.Check Version:
curl -k 'https://[ROUTER_IP]/downloadmaster/dm_apply.cgi?action_mode=initial&download_type=General&special_cgi=get_language' (Note: This may trigger the vulnerability)Verify Fix Applied:
After update, verify Download Master version shows 3.1.0.108 or higher in the router web interface.📡 Detection & Monitoring
Log Indicators:
- HTTP requests to /downloadmaster/dm_apply.cgi with action_mode=initial parameters
- Unusual access patterns to router web interface
Network Indicators:
- External IPs accessing router web interface on ports 80/443
- HTTP requests containing 'dm_apply.cgi' and 'get_language' parameters
SIEM Query:
source="router_logs" AND (uri_path="/downloadmaster/dm_apply.cgi" AND query_string="*action_mode=initial*")