CVE-2016-4521
📋 TL;DR
Sixnet BT-5xxx and BT-6xxx M2M devices contain hardcoded credentials that allow remote attackers to gain unauthorized access. This affects industrial control systems using these devices for machine-to-machine communication. Attackers can exploit this without authentication to compromise device functionality.
💻 Affected Systems
- Sixnet BT-5xxx M2M devices
- Sixnet BT-6xxx M2M devices
📦 What is this software?
Bt 5 Series Cellular Router Firmware by Sixnet
View all CVEs affecting Bt 5 Series Cellular Router Firmware →
Bt 5 Series Cellular Router Firmware by Sixnet
View all CVEs affecting Bt 5 Series Cellular Router Firmware →
⚠️ Risk & Real-World Impact
Worst Case
Complete device takeover allowing attackers to manipulate industrial processes, disrupt operations, or use devices as entry points into critical infrastructure networks.
Likely Case
Unauthorized access to device configuration, potential data exfiltration, and disruption of M2M communications in industrial environments.
If Mitigated
Limited impact if devices are behind firewalls with strict network segmentation and access controls, though risk remains if internal network is compromised.
🎯 Exploit Status
Exploitation requires only knowledge of hardcoded credentials, which are unspecified in public disclosure but likely known to attackers.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 3.8.21 or 3.9.8 and later
Vendor Advisory: https://ics-cert.us-cert.gov/advisories/ICSA-16-147-02
Restart Required: Yes
Instructions:
1. Download firmware version 3.8.21 or 3.9.8+ from vendor. 2. Backup device configuration. 3. Upload new firmware via web interface or CLI. 4. Reboot device. 5. Verify firmware version.
🔧 Temporary Workarounds
Network segmentation
allIsolate affected devices in separate VLANs with strict firewall rules limiting access to necessary services only.
Access control lists
allImplement IP-based access restrictions to limit which systems can communicate with vulnerable devices.
🧯 If You Can't Patch
- Implement strict network segmentation to isolate vulnerable devices from critical systems
- Monitor network traffic to/from affected devices for unauthorized access attempts
🔍 How to Verify
Check if Vulnerable:
Check device firmware version via web interface or CLI. If version is below 3.8.21 or between 3.9.0-3.9.7, device is vulnerable.Check Version:
Check via web interface at System > About, or via CLI with 'show version' commandVerify Fix Applied:
Confirm firmware version is 3.8.21 or higher, or 3.9.8 or higher. Test authentication with previously known hardcoded credentials should fail.📡 Detection & Monitoring
Log Indicators:
- Failed authentication attempts with hardcoded usernames
- Successful logins from unexpected IP addresses
- Configuration changes from unauthorized users
Network Indicators:
- Unusual traffic patterns to/from M2M devices
- Protocol anomalies in industrial communication
- Connections from unexpected network segments
SIEM Query:
source="sixnet-device" AND (event_type="authentication" AND result="success") | stats count by src_ip, user