CVE-2021-27710
📋 TL;DR
This CVE describes a critical command injection vulnerability in TOTOLINK routers that allows remote attackers to execute arbitrary operating system commands by sending specially crafted HTTP requests. The vulnerability affects TOTOLINK X5000R and A720R routers with specific firmware versions, enabling attackers to gain full control over affected devices. Attackers can exploit this without authentication by manipulating the 'ip' parameter in HTTP requests.
💻 Affected Systems
- TOTOLINK X5000R router
- TOTOLINK A720R router
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of router with persistent backdoor installation, credential theft, network pivoting to internal systems, and participation in botnets.
Likely Case
Router takeover for credential harvesting, DNS hijacking, man-in-the-middle attacks, and use as proxy for malicious activities.
If Mitigated
Limited impact if routers are behind firewalls with strict inbound filtering and network segmentation.
🎯 Exploit Status
Public exploit details available in referenced hackmd.io documents. Simple HTTP request manipulation required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: Not available
Restart Required: Yes
Instructions:
1. Check TOTOLINK website for firmware updates 2. Download latest firmware for your model 3. Access router admin interface 4. Navigate to firmware upgrade section 5. Upload and apply new firmware 6. Reboot router
🔧 Temporary Workarounds
Network Access Control
allRestrict access to router management interface using firewall rules
Management Interface Isolation
allMove router management interface to separate VLAN with strict access controls
🧯 If You Can't Patch
- Deploy network firewall with strict inbound rules blocking all unnecessary ports to router
- Implement network segmentation to isolate router from critical internal systems
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface. If version matches affected versions, device is vulnerable.Check Version:
Login to router admin interface and check System Status or Firmware Information pageVerify Fix Applied:
Verify firmware version has been updated to a version newer than affected versions.📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP requests to router management interface
- Commands containing shell metacharacters in HTTP parameters
- Multiple failed login attempts followed by successful command execution
Network Indicators:
- HTTP requests with shell commands in parameters (semicolons, pipes, backticks)
- Outbound connections from router to suspicious IPs
- Unusual traffic patterns from router
SIEM Query:
source="router_logs" AND (http_request CONTAINS ";" OR http_request CONTAINS "|" OR http_request CONTAINS "`") AND http_uri CONTAINS "/cgi-bin/"