CVE-2021-29294
📋 TL;DR
A null pointer dereference vulnerability in D-Link DSL-2740R routers allows remote attackers to cause denial of service by sending crafted POST requests to the /HNAP1/ endpoint. This affects all hardware revisions of the DSL-2740R UK_1.01 firmware. The device is end-of-life and will not receive patches.
💻 Affected Systems
- D-Link DSL-2740R
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device crash requiring physical reboot, disrupting all network services for connected users.
Likely Case
Temporary service interruption affecting web interface and potentially network connectivity until device reboots.
If Mitigated
No impact if device is not internet-facing and network access is properly restricted.
🎯 Exploit Status
Simple HTTP POST request triggers the vulnerability. No authentication required.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: N/A
Vendor Advisory: https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10213
Restart Required: No
Instructions:
No official patch available. Device is End of Life. Replace with supported hardware.
🔧 Temporary Workarounds
Block HNAP1 Interface
linuxUse firewall rules to block access to /HNAP1/ endpoint
iptables -A INPUT -p tcp --dport 80 -m string --string "POST /HNAP1/" --algo bm -j DROP
Disable Remote Management
allTurn off remote administration in router settings
🧯 If You Can't Patch
- Replace device with supported hardware
- Isolate device behind firewall with strict inbound rules
🔍 How to Verify
Check if Vulnerable:
Check router web interface for firmware version UK_1.01Check Version:
curl -s http://router-ip/ | grep -i firmwareVerify Fix Applied:
No fix available. Verify device replacement or workaround implementation.📡 Detection & Monitoring
Log Indicators:
- Multiple POST requests to /HNAP1/ endpoint
- Router reboot events
Network Indicators:
- HTTP POST to /HNAP1/ with crafted payload
- Sudden loss of router connectivity
SIEM Query:
source="router_logs" AND (uri="/HNAP1/" OR message="reboot")