Critical Telnet Backdoor in Shenzhen Liandian IP Cameras

Critical Vulnerability in Shenzhen Liandian IP Cameras

Overview

A critical security flaw, tracked as CVE-2025-7503, has been discovered in an OEM IP camera manufactured by Shenzhen Liandian Communication Technology LTD. The vulnerability allows attackers to gain root-level access via an undocumented Telnet service with default credentials.

With a CVSS v3.1 base score of 10.0 (CRITICAL), this flaw enables remote code execution (RCE) and privilege escalation, posing severe risks to affected devices.

Technical Details

Affected Firmware & Hardware 

• Firmware Version: AppFHE1_V1.0.6.0
• Kernel Version: KerFHE1_PTZ_WIFI_V3.1.1
• Hardware Model: HwFHE1_WF6_PTZ_WIFI_20201218

Vulnerability Breakdown

1. Undocumented Telnet Service (Port 23)

   • The Telnet service is enabled by default but not mentioned in the device’s documentation or web interface.

   • No option to disable it via the admin panel.

2. Hardcoded Default Credentials 

   • Attackers can log in using undocumented default credentials (e.g., root:admin or similar).

   • Successful authentication provides root shell access, allowing full control over the device.

3. No Official Patch Available

   • The vendor (Shenzhen Liandian) has not released a firmware update.

   • Attempts to contact the vendor were unsuccessful.

Attack Scenarios

Scenario 1: Mass Exploitation in a Botnet

An attacker scans the internet for vulnerable IP cameras using Shodan or Censys, identifying devices with port 23 open.

1. The attacker uses a simple script to brute-force common default credentials.
2. Upon successful login, they deploy a Mirai-like botnet payload, turning the camera into a DDoS zombie.
3. The compromised device then participates in large-scale attacks against other targets.

Impact:

• Thousands of cameras could be weaponized for cyberattacks.
• Network performance degradation due to botnet traffic.

Scenario 2: Corporate Espionage via Compromised Surveillance

A malicious insider or external hacker targets a company using these cameras for security monitoring.

1. The attacker gains access via Telnet and escalates privileges to root.
2. They install a backdoor to maintain persistence.
3. The attacker intercepts video feeds, disables recording, or even spies on sensitive areas.

Impact:

• Loss of confidential visual data.
• Physical security breach due to disabled surveillance.

Mitigation & Workarounds

Since no official patch exists, users should:

1. Disable Telnet via Firewall Rules

   • Block inbound/outbound traffic on port 23 at the network level.

   • Example (Linux iptables):

     bash

     iptables -A INPUT -p tcp --dport 23 -j DROP

2. Isolate Cameras on a Separate VLAN

   • Restrict camera communication to only necessary services.

3. Monitor for Unusual Activity

   • Check logs for unexpected Telnet login attempts.

4. Consider Replacing Vulnerable Devices

   • If possible, switch to a vendor that provides security updates.

Conclusion

CVE-2025-7503 is a severe vulnerability that exposes Shenzhen Liandian IP cameras to complete remote takeover. Given the lack of vendor support, organizations must take proactive measures to secure affected devices before they are exploited in real-world attacks.

Timeline:

• Discovered: July 2025
• Published: July 11, 2025
• Status: Unpatched (as of publication)

Additional Resources

• https://nvd.nist.gov/