CVE-2025-5621
📋 TL;DR
This critical vulnerability in D-Link DIR-816 routers allows remote attackers to execute arbitrary operating system commands via command injection in the qosClassifier function. Attackers can exploit this by manipulating dip_address or sip_address parameters in requests to /goform/qosClassifier. Only unsupported D-Link DIR-816 routers running specific firmware versions are affected.
💻 Affected Systems
- D-Link DIR-816
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of the router allowing attackers to install persistent backdoors, intercept all network traffic, pivot to internal networks, and use the device for botnet activities.
Likely Case
Remote code execution leading to router configuration changes, credential theft, DNS hijacking, and participation in DDoS attacks.
If Mitigated
Limited impact if router is behind firewall with restricted WAN access, though internal attackers could still exploit.
🎯 Exploit Status
Public exploit code available on GitHub. Attack requires sending crafted HTTP POST request to vulnerable endpoint.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: None
Vendor Advisory: https://www.dlink.com/
Restart Required: No
Instructions:
No official patch available as product is end-of-life. Replace affected hardware with supported models.
🔧 Temporary Workarounds
Disable QoS functionality
allTurn off Quality of Service features in router web interface to potentially disable vulnerable endpoint
Block access to vulnerable endpoint
linuxUse firewall rules to block access to /goform/qosClassifier
iptables -A INPUT -p tcp --dport 80 -m string --string "/goform/qosClassifier" --algo bm -j DROP
iptables -A INPUT -p tcp --dport 443 -m string --string "/goform/qosClassifier" --algo bm -j DROP
🧯 If You Can't Patch
- Immediately replace affected D-Link DIR-816 routers with supported hardware
- Isolate affected routers in separate VLAN with strict firewall rules preventing internet access
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in web interface under Maintenance > Firmware. If version is 1.10CNB05, device is vulnerable.Check Version:
curl -s http://router-ip/ | grep -i firmware or check web interfaceVerify Fix Applied:
No fix available to verify. Replacement with different hardware is the only solution.📡 Detection & Monitoring
Log Indicators:
- HTTP POST requests to /goform/qosClassifier with unusual dip_address or sip_address parameters
- Unusual command execution in router logs
- Failed authentication attempts followed by qosClassifier access
Network Indicators:
- HTTP traffic to router on port 80/443 containing qosClassifier in URI with shell metacharacters in parameters
- Outbound connections from router to suspicious IPs
SIEM Query:
source="router_logs" AND (uri="/goform/qosClassifier" OR (uri CONTAINS "qosClassifier" AND (param CONTAINS ";" OR param CONTAINS "|" OR param CONTAINS "`")))