How to remediate – WordPress User Registration Form Detected

1. Introduction

The WordPress User Registration Form Detected vulnerability means a publicly accessible form allowing new user accounts has been found on your website. This presents an attacker with a potential entry point for malicious activity, such as account takeover or denial of service through resource exhaustion. Typically affects websites running the WordPress content management system (CMS) with registration enabled. A successful exploit could compromise confidentiality, integrity and availability of user data and services.

2. Technical Explanation

The vulnerability occurs because a standard WordPress User Registration Form is exposed without restriction. An attacker can attempt to create numerous accounts using automated tools. This may lead to brute-force attacks or dictionary attacks against the registration form. No specific CVE, CVSS, or CWE are directly associated with simply detecting an open registration form; however, exploitation of that form would fall under common attack patterns covered by these standards.

• Root cause: The publicly accessible User Registration Form lacks sufficient access controls.
• Exploit mechanism: An attacker uses a script to repeatedly submit registration requests with different credentials in an attempt to guess valid usernames and passwords, or simply overwhelm the system. For example, using a tool like Hydra to brute-force the form.
• Scope: WordPress installations with publicly accessible User Registration Forms are affected. This includes all versions of WordPress where user registration is enabled by default or through plugins.

3. Detection and Assessment

Confirming the vulnerability involves checking for a public registration page on your WordPress site. A thorough assessment requires reviewing access logs.

• Quick checks: Visit your website’s registration page (usually /wp-login.php?action=register or similar). If accessible without authentication, it is likely vulnerable.
• Scanning: Nessus plugin ID 16389 can identify open WordPress Registration Forms as an example.
• Logs and evidence: Check your web server access logs for requests to the registration page from unknown IP addresses. Look for patterns of repeated POST requests to this endpoint.

curl -I https://yourwebsite.com/wp-login.php?action=register

4. Solution / Remediation Steps

Restrict access to the Registration Form using a .htaccess file, limiting access to known IP Addresses.

4.1 Preparation

• No services need stopping for this fix.
• Roll back plan: Remove or comment out the added .htaccess rules if issues occur. Change window is not required, but recommended during low traffic periods.

4.2 Implementation

1. Step 1: Edit your website’s root directory .htaccess file.
2. Step 2: Add the following code to restrict access to known IP addresses. Replace ‘your_allowed_ip’ with the actual IP address(es) that should have access. Multiple IPs can be added on separate lines.

4.3 Config or Code Example

Before

# No specific rules for registration form access

After

<Files wp-login.php?action=register>
  Order Deny,Allow
  Deny from all
  Allow from your_allowed_ip
</Files>

4.4 Security Practices Relevant to This Vulnerability

List only practices that directly address this vulnerability type. Use neutral wording and examples instead of fixed advice.

• Practice 1: Least privilege – restrict access to sensitive resources like registration forms to authorized IP addresses or networks.
• Practice 2: Input validation – while not a direct fix for an open form, validating user input can mitigate the impact if exploitation occurs.

4.5 Automation (Optional)

No suitable automation script is available due to the need for specific IP address configuration.

5. Verification / Validation

Confirm the fix by attempting to access the registration page from an unauthorized IP address and verifying that it is blocked. Then, test access from a permitted IP.

• Post-fix check: Attempt to access https://yourwebsite.com/wp-login.php?action=register from an unapproved IP address. You should receive a ‘403 Forbidden’ error.
• Re-test: Re-run the quick check (Section 3) from an unauthorized IP address to confirm it is blocked.
• Smoke test: Verify that users with approved IPs can still log in and access other website features.
• Monitoring: Check web server logs for denied requests to the registration page, indicating successful blocking of unauthorized access.

curl -I https://yourwebsite.com/wp-login.php?action=register

6. Preventive Measures and Monitoring

Suggest only measures that are relevant to the vulnerability type.

• Baselines: Update your security baseline to include a requirement for restricting access to sensitive WordPress pages, such as registration forms.
• Pipelines: Implement regular security scans of your WordPress installation to identify open registration forms or other vulnerabilities.
• Asset and patch process: Review WordPress configurations regularly to ensure that access controls are properly configured.

7. Risks, Side Effects, and Roll Back

List known risks or service impacts from the change.

• Roll back: Remove or comment out the added lines in your .htaccess file.

8. References and Resources

Link only to sources that match this exact vulnerability.

• Vendor advisory or bulletin: https://codex.wordpress.org/htaccess
• NVD or CVE entry: Not applicable for detection of an open form.
• Product or platform documentation relevant to the fix: https://codex.wordpress.org/htaccess