CVE-2017-7964
📋 TL;DR
Zyxel WRE6505 devices have a default TELNET password of '1234' for root and admin accounts, allowing remote attackers to gain administrative access. This enables DNS hijacking attacks by reconfiguring the built-in dnshijacker process. All Zyxel WRE6505 devices using default credentials are affected.
💻 Affected Systems
- Zyxel WRE6505
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise leading to DNS hijacking, man-in-the-middle attacks, credential theft, and potential lateral movement into connected networks.
Likely Case
Remote attackers gain administrative access to reconfigure DNS settings, redirecting users to malicious sites for phishing or malware distribution.
If Mitigated
If default credentials are changed, the vulnerability is effectively neutralized with minimal impact.
🎯 Exploit Status
Exploitation requires only TELNET access and knowledge of default password. No special tools or skills needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: N/A
Vendor Advisory: Not publicly available
Restart Required: No
Instructions:
1. Access device administration interface
2. Navigate to TELNET/remote access settings
3. Change default password for root and admin accounts to strong, unique passwords
4. Disable TELNET if not required, use SSH instead
🔧 Temporary Workarounds
Disable TELNET service
allCompletely disable TELNET access to prevent remote exploitation
telnet_disable
service telnet stop
Network access control
linuxRestrict TELNET access to trusted IP addresses only
iptables -A INPUT -p tcp --dport 23 -s [TRUSTED_IP] -j ACCEPT
iptables -A INPUT -p tcp --dport 23 -j DROP
🧯 If You Can't Patch
- Isolate affected devices in separate network segments with strict firewall rules
- Implement network monitoring for TELNET connections and DNS configuration changes
🔍 How to Verify
Check if Vulnerable:
Attempt TELNET connection to device port 23 using username 'root' or 'admin' with password '1234'Check Version:
show version (via TELNET or web interface)Verify Fix Applied:
Verify TELNET login fails with old password and succeeds only with new credentials📡 Detection & Monitoring
Log Indicators:
- Failed/successful TELNET authentication attempts
- DNS configuration changes in system logs
Network Indicators:
- Unexpected TELNET connections from external IPs
- DNS queries to unusual or malicious domains
SIEM Query:
source="device_logs" (event="telnet_login" AND (user="root" OR user="admin")) OR event="dns_config_change"