CVE-2021-27113
📋 TL;DR
This vulnerability allows remote attackers to execute arbitrary commands on D-Link DIR-816 A2 routers by injecting shell metacharacters into HTTP parameters. Attackers can gain full control of affected devices, potentially compromising network security. Only DIR-816 A2 routers running firmware version 1.10 B05 are affected.
💻 Affected Systems
- D-Link DIR-816 A2
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device takeover leading to network compromise, data exfiltration, malware deployment, and use as attack platform
Likely Case
Router compromise allowing traffic interception, credential theft, and lateral movement within network
If Mitigated
Limited impact if device is behind firewall with restricted HTTP access
🎯 Exploit Status
Simple HTTP request with command injection payload to /goform/addRouting endpoint
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check vendor for latest firmware
Vendor Advisory: https://www.dlink.com/en/security-bulletin/
Restart Required: Yes
Instructions:
1. Visit D-Link support site 2. Download latest firmware for DIR-816 A2 3. Log into router admin interface 4. Navigate to firmware update section 5. Upload and apply new firmware 6. Reboot router
🔧 Temporary Workarounds
Disable remote administration
allPrevent external access to router web interface
Network segmentation
allIsolate router management interface from untrusted networks
🧯 If You Can't Patch
- Replace affected device with supported model
- Place router behind dedicated firewall with strict HTTP access controls
🔍 How to Verify
Check if Vulnerable:
Check firmware version in router admin interface under System Status or ToolsCheck Version:
curl -s http://router-ip/status.asp | grep -i firmwareVerify Fix Applied:
Confirm firmware version is updated beyond 1.10 B05📡 Detection & Monitoring
Log Indicators:
- HTTP requests to /goform/addRouting with shell metacharacters
- Unusual command execution in system logs
Network Indicators:
- HTTP POST requests to router IP on port 80 with command injection patterns
- Outbound connections from router to unexpected destinations
SIEM Query:
source="router.log" AND (uri="/goform/addRouting" AND (content="|" OR content=";" OR content="`" OR content="$"))