How to remediate – Alcatel ADSL Modem Unpassworded Access

1. Introduction

The Alcatel ADSL Modem Unpassworded Access vulnerability allows an attacker to gain unauthorized access to your modem due to a missing password. This could allow them to reconfigure your internet connection, potentially locking you out of service. This affects Alcatel ADSL modems with default or no passwords set on their accounts, impacting the confidentiality, integrity and availability of your internet connectivity.

2. Technical Explanation

The vulnerability exists because the modem ships with an account that has no password configured. An attacker can use Telnet to connect to the modem remotely and gain full administrative access. This allows them to change settings, including the administrator password and internet connection details. CVE-2001-1424 describes this issue.

• Root cause: The modem account has no default password set, allowing anyone with network access to connect without authentication.
• Exploit mechanism: An attacker uses Telnet to connect to the modem’s management interface and execute commands as an administrator. For example, they could use a simple Telnet client to connect on port 23 and then issue commands to change the password or DNS settings.
• Scope: Alcatel ADSL modems are affected. Specific models were not detailed in available documentation.

3. Detection and Assessment

You can confirm if your modem is vulnerable by checking for a default account with no password set, or attempting to connect using Telnet without credentials.

• Scanning: Nessus plugin ID 30457 can detect this vulnerability. This is an example only and may require updating to reflect current signatures.
• Logs and evidence: Modem logs may show successful Telnet connections from unknown sources if the modem has been compromised. Check for login attempts without valid credentials, though logging may be limited on these devices.

telnet <modem_ip_address>

4. Solution / Remediation Steps

Set a strong password on the modem’s administrator account immediately to prevent unauthorized access.

4.1 Preparation

• Dependencies: You will need Telnet client software installed on your computer. Roll back is possible by resetting the modem to factory defaults (consult the modem’s documentation).
• Change window needs and approvals are not usually required for this simple change, but it’s good practice to inform users of potential brief internet connectivity interruptions.

4.2 Implementation

1. Step 1: Telnet to your modem’s IP address (usually 192.168.1.1).
2. Step 2: If prompted for a username, enter the default administrator username (often ‘admin’).
3. Step 3: When prompted for a password, leave it blank and press Enter.
4. Step 4: Once logged in, navigate to the administration or system settings menu. The exact path varies by model.
5. Step 5: Change the administrator password to a strong, unique value.
6. Step 6: Save the changes and reboot the modem if prompted.

4.3 Config or Code Example

Before

Login: admin
Password: 

After

Login: admin
Password: <your_strong_password>

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this type of issue. Least privilege is important, as limiting access reduces the impact if an account is compromised. Safe defaults are also crucial – devices should not ship with blank or easily guessable passwords.

• Practice 1: Implement least privilege by creating separate accounts for different administrative tasks and restricting their permissions.
• Practice 2: Enforce strong password policies, requiring complex passwords that are regularly changed.

4.5 Automation (Optional)

Automation is not typically feasible for this specific vulnerability due to the manual configuration required on each device.

5. Verification / Validation

Confirm the fix by attempting to connect via Telnet with the new password. A negative test would be an unsuccessful login attempt using the old, blank password.

• Post-fix check: Attempt to telnet to the modem’s IP address and enter the new administrator password when prompted. Successful login confirms the fix.
• Re-test: Repeat the initial detection method (attempting Telnet without credentials). You should now be prompted for a password, indicating that the vulnerability is resolved.
• Monitoring: Monitor modem logs for failed login attempts from unknown sources as an indicator of potential brute-force attacks.

telnet <modem_ip_address>
Login: admin
Password: <your_strong_password> 

6. Preventive Measures and Monitoring

Updating security baselines to include strong password requirements can help prevent this issue. Regularly reviewing device configurations during deployment is also important.

• Baselines: Update your network security baseline or policy to require all devices to have strong passwords set by default.
• Asset and patch process: Implement a regular review cycle for device configurations, especially on internet-facing equipment.

7. Risks, Side Effects, and Roll Back

• Risk or side effect 1: Incorrectly entered password may require a factory reset.

8. References and Resources

Links only to sources that match this exact vulnerability. Use official advisories and trusted documentation. Do not include generic links.

• Vendor advisory or bulletin: No specific vendor advisory was found for all Alcatel ADSL modems, but general security information is available on their website.
• NVD or CVE entry: CVE-2001-1424
• Product or platform documentation relevant to the fix: Consult your specific Alcatel ADSL modem’s user manual for instructions on changing the administrator password.