CVE-2021-43722
📋 TL;DR
This vulnerability in D-Link DIR-645 routers allows remote attackers to execute arbitrary code via a buffer overflow in the HNAP service. Attackers can exploit this by sending specially crafted SOAPAction headers to trigger the overflow. All users of affected DIR-645 router versions are at risk.
💻 Affected Systems
- D-Link DIR-645 Wireless N300 Router
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with root privileges leading to complete device compromise, network infiltration, and persistent backdoor installation.
Likely Case
Remote code execution allowing attackers to modify router settings, intercept traffic, or join the device to a botnet.
If Mitigated
Denial of service if exploit fails or is blocked, potentially crashing the router service.
🎯 Exploit Status
Public exploit code exists in GitHub repositories. The vulnerability requires no authentication and has straightforward 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. Visit D-Link support website. 2. Download latest firmware for DIR-645. 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 Management
allPrevent external access to the vulnerable HNAP service
Log into router admin -> Advanced -> Remote Management -> Disable
Block HNAP Service
linuxUse firewall rules to block access to port 80 on the router
iptables -A INPUT -p tcp --dport 80 -j DROP
🧯 If You Can't Patch
- Segment the router on isolated network segment with strict firewall rules
- Replace with a supported router model that receives security updates
🔍 How to Verify
Check if Vulnerable:
Check router firmware version in admin interface matches affected version 1.03 A1Check Version:
Log into router admin interface and check System Info or Status pageVerify Fix Applied:
Verify firmware version has been updated to a version after the patch release📡 Detection & Monitoring
Log Indicators:
- Unusual SOAPAction header lengths in HTTP requests
- Router service crashes or restarts
Network Indicators:
- HTTP requests with abnormally long SOAPAction headers to router port 80
- Exploit pattern matches in network traffic
SIEM Query:
source="router_logs" AND (http_user_agent="*overflow*" OR http_request="*SOAPAction:*" AND length(http_request)>500)