CVE-2021-26810
📋 TL;DR
CVE-2021-26810 is a remote command injection vulnerability in D-Link DIR-816 A2 routers that allows attackers to execute arbitrary commands on the device. The vulnerability exists in the web interface's /goform/dir_setWanWifi handler where user input is improperly sanitized. This affects all users of DIR-816 A2 routers with vulnerable firmware.
💻 Affected Systems
- D-Link DIR-816 A2
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing attacker to install persistent backdoors, intercept network traffic, pivot to internal networks, or brick the device.
Likely Case
Attacker gains shell access to router, modifies network settings, intercepts traffic, or uses device as botnet node.
If Mitigated
Limited impact if device is behind firewall with restricted WAN access and proper network segmentation.
🎯 Exploit Status
Public exploit code exists in GitHub repositories. Simple HTTP request with shell metacharacters can trigger exploitation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check D-Link support for latest firmware
Vendor Advisory: https://www.dlink.com/en/security-bulletin/
Restart Required: Yes
Instructions:
1. Log into router web interface. 2. Navigate to Firmware Update section. 3. Download latest firmware from D-Link support site. 4. Upload and apply firmware update. 5. Reboot router.
🔧 Temporary Workarounds
Disable Remote Management
allPrevent external access to router web interface
Restrict Web Interface Access
linuxUse firewall rules to limit access to router management interface
iptables -A INPUT -p tcp --dport 80 -s trusted_ip -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Replace vulnerable router with supported model
- Place router behind dedicated firewall with strict access controls
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in web interface under Tools > FirmwareCheck Version:
curl -s http://router_ip/goform/getStatus | grep firmwareVerify Fix Applied:
Verify firmware version is newer than v1.10 and test with known exploit payloads📡 Detection & Monitoring
Log Indicators:
- HTTP requests to /goform/dir_setWanWifi with shell metacharacters in parameters
- Unusual command execution in router logs
Network Indicators:
- HTTP POST requests to router IP on port 80 with suspicious parameter values
- Outbound connections from router to unknown IPs
SIEM Query:
source="router_logs" AND (uri="/goform/dir_setWanWifi" AND (param="statuscheckpppoeuser" AND value MATCHES "[;&|`$()]"))