How to remediate – Grandstream Phone Web Interface Detection

1. Introduction

The Grandstream Phone Web Interface Detection vulnerability indicates that a web interface for a Grandstream phone is accessible on the network. This means an attacker could potentially access configuration settings and compromise the device. Businesses should address this as it can lead to loss of confidentiality, integrity, and availability of voice communications.

2. Technical Explanation

Nessus detected a web interface associated with Grandstream phones. The default configuration often leaves the web interface exposed, allowing unauthenticated access to sensitive settings. An attacker could exploit this by changing phone configurations, intercepting calls, or gaining control of the device. There is no CVE currently associated with this detection.

• Root cause: The web interface for Grandstream phones is accessible without authentication.
• Exploit mechanism: An attacker can access the web interface via a web browser and modify phone settings. For example, they could change call forwarding rules or redirect calls to malicious numbers.
• Scope: All Grandstream phones with an exposed web interface are affected.

3. Detection and Assessment

You can confirm if a system is vulnerable by checking for the presence of the web interface on your network. A thorough method involves attempting to access the interface directly.

• Quick checks: Use ping followed by browsing to http:// in a web browser. If you see the Grandstream phone login page, it is likely vulnerable.
• Scanning: Nessus plugin ID 93854 can detect this vulnerability.
• Logs and evidence: Check firewall logs for connections to port 80 or 443 on known Grandstream phone IP addresses.

ping 

4. Solution / Remediation Steps

The following steps outline how to fix the issue.

4.1 Preparation

• Dependencies: Access to the Grandstream phone’s web interface is required. Change windows may be needed depending on business impact.

4.2 Implementation

1. Step 1: Log in to the Grandstream phone’s web interface using administrator credentials.
2. Step 2: Navigate to the “Security” or “Administration” section of the web interface.
3. Step 3: Disable remote management access, if possible. If disabling is not an option, restrict access by IP address to only trusted networks.
4. Step 4: Change the default administrator password to a strong, unique password.
5. Step 5: Save the changes and reboot the phone if prompted.

4.3 Config or Code Example

Before

Remote Management: Enabled

After

Remote Management: Disabled

4.4 Security Practices Relevant to This Vulnerability

• Practice 1: Least privilege – restrict access to the phone’s web interface to only authorized personnel and networks.
• Practice 2: Strong passwords – use strong, unique passwords for all administrator accounts.

4.5 Automation (Optional)

Automation is not generally suitable for this vulnerability due to the need for per-device configuration changes.

5. Verification / Validation

Confirm that the fix worked by checking if remote management access has been disabled or restricted.

• Post-fix check: Attempt to access the web interface from an untrusted network. You should no longer be able to connect, or you should be prompted for credentials.
• Re-test: Re-run Nessus scan 93854. The vulnerability should no longer be reported.
• Monitoring: Monitor firewall logs for any unauthorized access attempts to port 80 or 443 on Grandstream phone IP addresses.

Attempt to browse to http:// from an untrusted network - should be blocked.

6. Preventive Measures and Monitoring

• Baselines: Update your security baseline or policy to require strong passwords and disable remote management access on all Grandstream phones.
• Asset and patch process: Review phone configurations regularly as part of an asset management program.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Disabling remote management may require local access for configuration changes.
• Risk or side effect 2: Incorrectly configured IP restrictions could block legitimate access.

8. References and Resources

• Vendor advisory or bulletin: http://www.grandstream.com/