How to remediate – 602LAN SUITE Open Telnet Proxy

1. Introduction

The 602LAN SUITE Open Telnet Proxy vulnerability allows remote attackers to use a server running 602LAN SUITE as a proxy, potentially launching attacks that appear to originate from the host network and accessing internal resources. This poses a risk to confidentiality, integrity, and availability of systems on the internal network. Affected systems are those running 602LAN SUITE with the Telnet server proxy enabled. Impact is likely to be medium due to potential for lateral movement within an organisation’s network.

2. Technical Explanation

The vulnerability occurs because 602LAN SUITE runs an open Telnet server that can act as a proxy. An attacker can connect to this Telnet proxy and relay connections through it, masking their origin IP address. This could allow them to bypass firewalls or access resources only available on the internal network. There is no known CVE associated with this specific issue. A realistic example would be an attacker using the proxy to scan internal systems that are not directly accessible from the internet.

• Root cause: The Telnet server proxy feature is enabled by default and does not require strong authentication or authorization.
• Exploit mechanism: An attacker connects to the open Telnet port on the target system, establishes a connection as a SOCKS proxy, and then uses this proxy to connect to internal resources.
• Scope: Systems running 602LAN SUITE with the Telnet server proxy enabled are affected.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking for an open port on the target host, or looking at configuration files.

• Quick checks: Use `telnet 23` to check if port 23 (Telnet) is open. If it connects, the proxy may be running.
• Scanning: Nessus plugin ID 10468 can detect this vulnerability. This is an example only and other scanners may also provide detection capabilities.
• Logs and evidence: Check system logs for connections to port 23 from unexpected sources.

telnet  23

4. Solution / Remediation Steps

Disable the Telnet server proxy within the 602LAN SUITE configuration.

4.1 Preparation

• Ensure you have access to the 602LAN SUITE configuration interface or files. A roll back plan is to restore from the snapshot taken earlier.

4.2 Implementation

1. Step 1: Log in to the 602LAN SUITE administration interface.
2. Step 2: Navigate to the Telnet server settings.
3. Step 3: Disable the Telnet server proxy feature.
4. Step 4: Save the changes and restart the 602LAN SUITE service.

4.3 Config or Code Example

Before

EnableTelnetProxy = True

After

EnableTelnetProxy = False

4.4 Security Practices Relevant to This Vulnerability

Practices that address this vulnerability include least privilege and secure defaults.

• Practice 1: Least privilege – limiting the services running on a system reduces the attack surface.
• Practice 2: Secure defaults – disabling unnecessary features by default prevents accidental exposure of vulnerabilities.

4.5 Automation (Optional)

# Example PowerShell script to disable Telnet service (use with caution)
Stop-Service -Name "602LANSUITE" -Force
Set-Service -Name "602LANSUITE" -StartupType Disabled

5. Verification / Validation

Confirm the fix by checking that port 23 is no longer open and re-running the initial detection method.

• Post-fix check: Run `telnet 23`. The connection should be refused or time out.
• Re-test: Re-run the `telnet 23` command; it should no longer connect.
• Smoke test: Verify that other 602LAN SUITE functions are still working as expected.
• Monitoring: Monitor system logs for any unexpected connections to port 23, which could indicate a regression.

telnet  23

6. Preventive Measures and Monitoring

Update security baselines and implement regular patch cycles to prevent similar issues. For example, ensure CIS control 5 covers unnecessary services.

• Baselines: Update your security baseline or policy to include a requirement for disabling unused services like Telnet.
• Pipelines: Add checks in CI/CD pipelines to scan for open ports and vulnerable configurations.
• Asset and patch process: Implement a regular patch cycle to ensure systems are up-to-date with the latest security fixes.

7. Risks, Side Effects, and Roll Back

Disabling the Telnet server proxy may affect any applications or services that rely on it. The roll back steps involve re-enabling the Telnet server proxy in the 602LAN SUITE configuration and restarting the service.

• Risk or side effect 1: Disabling the Telnet proxy could break compatibility with legacy systems relying on it.
• Risk or side effect 2: Restarting the 602LAN SUITE service may cause a brief interruption of service.
• Roll back:
  1. Step 1: Log in to the 602LAN SUITE administration interface.
  2. Step 2: Navigate to the Telnet server settings.
  3. Step 3: Re-enable the Telnet server proxy feature.
  4. Step 4: Save the changes and restart the 602LAN SUITE service.

8. References and Resources

• Vendor advisory or bulletin: No specific vendor advisory available for this issue, consult 602LAN SUITE documentation.
• NVD or CVE entry: No CVE associated with this specific issue.
• Product or platform documentation relevant to the fix: Refer to the official 602LAN SUITE configuration guide for instructions on disabling the Telnet server proxy.