CVE-2018-20432
📋 TL;DR
This vulnerability allows unauthenticated attackers to gain privileged telnet access to affected D-Link routers using hardcoded credentials. Attackers can extract sensitive data, modify router configurations, or potentially pivot to internal networks. Users of D-Link COVR-2600R and COVR-3902 Kit routers with firmware before version 1.01b05Beta01 are affected.
💻 Affected Systems
- D-Link COVR-2600R
- D-Link COVR-3902 Kit
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete router compromise allowing attackers to intercept all network traffic, install persistent backdoors, pivot to internal devices, and permanently disable router functionality.
Likely Case
Attackers gain administrative access to modify DNS settings, redirect traffic to malicious sites, steal credentials, and disable security features.
If Mitigated
Limited impact with proper network segmentation, firewall rules blocking telnet from untrusted networks, and monitoring for unauthorized access attempts.
🎯 Exploit Status
Exploitation requires only telnet access to the router and knowledge of the hardcoded credentials. Public exploit code and detailed analysis are available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.01b05Beta01 and later
Vendor Advisory: https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10109
Restart Required: Yes
Instructions:
1. Download firmware version 1.01b05Beta01 or later from D-Link support site. 2. Log into router web interface. 3. Navigate to System Tools > Firmware Upgrade. 4. Upload and install the new firmware. 5. Router will reboot automatically.
🔧 Temporary Workarounds
Disable Telnet Service
allDisable telnet access to prevent exploitation via this service
telnetd -l /bin/sh -p 23 & (to check if running)
killall telnetd (to stop service)
Remove telnet startup from init scripts
Block Telnet at Firewall
allConfigure firewall to block telnet port 23 from untrusted networks
iptables -A INPUT -p tcp --dport 23 -j DROP (Linux)
netsh advfirewall firewall add rule name="Block Telnet" dir=in action=block protocol=TCP localport=23 (Windows)
🧯 If You Can't Patch
- Isolate affected routers in separate VLAN with strict firewall rules
- Implement network monitoring for telnet connection attempts and alert on successful logins
🔍 How to Verify
Check if Vulnerable:
Attempt telnet connection to router port 23 using known hardcoded credentials (publicly documented in exploit references). Successful login indicates vulnerability.Check Version:
telnet [router_ip] 23, then login and run 'cat /proc/version' or check web interface System StatusVerify Fix Applied:
After patching, attempt telnet login with hardcoded credentials - should fail. Check firmware version matches 1.01b05Beta01 or later.📡 Detection & Monitoring
Log Indicators:
- Successful telnet logins from unexpected IP addresses
- Multiple failed telnet login attempts followed by success
- Configuration changes via telnet session
Network Indicators:
- Telnet connections to router port 23 from external IPs
- Unusual outbound traffic patterns after telnet access
- DNS configuration changes
SIEM Query:
source="router_logs" (event="telnet login successful" OR event="configuration modified") | stats count by src_ip🔗 References
- http://packetstormsecurity.com/files/159058/COVR-3902-1.01B0-Hardcoded-Credentials.html
- https://cybersecurityworks.com/zerodays/cve-2018-20432-dlink.html
- https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10109
- http://packetstormsecurity.com/files/159058/COVR-3902-1.01B0-Hardcoded-Credentials.html
- https://cybersecurityworks.com/zerodays/cve-2018-20432-dlink.html
- https://supportannouncement.us.dlink.com/announcement/publication.aspx?name=SAP10109
