How to remediate – WordPress User Enumeration

1. Introduction

WordPress User Enumeration is a vulnerability where an attacker can discover valid usernames on a WordPress website without needing to be logged in. This allows attackers to build lists of potential credentials for brute force attacks, increasing the risk of account takeover. Systems running vulnerable versions of WordPress are affected. Confidentiality may be impacted due to user information disclosure.

2. Technical Explanation

The vulnerability arises from a lack of rate limiting or other protections on the author archive pages in WordPress. An attacker can systematically request pages for different usernames, and if a page exists, it confirms that username is valid. This isn’t a direct code flaw but an information leak due to how WordPress handles user profiles. There is no specific CVE currently associated with this issue.

• Root cause: Missing rate limiting on author archive pages allows enumeration of usernames.
• Exploit mechanism: An attacker iterates through potential usernames, checking for the existence of corresponding author archive pages (e.g., https://example.com/author/username). A successful response indicates a valid user.
• Scope: WordPress versions prior to those with appropriate security measures are affected.

3. Detection and Assessment

You can confirm if your system is vulnerable by checking the version of WordPress installed, and then testing for username enumeration.

• Quick checks: Check the WordPress version in the admin dashboard (Settings > General). Look for a readme.html file in the root directory which also contains the version number.
• Scanning: Nessus plugin ID 16387 can identify this vulnerability as an example.
• Logs and evidence: Access logs may show repeated requests to author archive pages, potentially indicating enumeration attempts.

curl -I https://example.com/author/testuser

4. Solution / Remediation Steps

The following steps will help you fix the issue.

4.1 Preparation

• No services need to be stopped for this remediation.

4.2 Implementation

1. Step 1: Install a WordPress security plugin that includes user enumeration protection (e.g., Wordfence, Sucuri Security).
2. Step 2: Configure the plugin to block access to author archive pages for unauthenticated users.
3. Step 3: Test the fix by attempting to access an author archive page without being logged in; it should return a 403 Forbidden error or redirect.

4.3 Config or Code Example

Before

# No specific configuration - author archive pages are publicly accessible by default

After

# Wordfence settings (example)
# Block access to author archives for non-logged in users. 
# Configure the plugin's firewall rules accordingly.

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. For example: least privilege, input validation, safe defaults, secure headers, patch cadence. If a practice does not apply, do not include it.

• Practice 1: Least privilege – limit user access to only what is needed to reduce the impact if an account is compromised.
• Practice 2: Input validation – ensure all inputs are properly validated and sanitized to prevent unexpected behaviour.

4.5 Automation (Optional)

# No automation script provided as this is best handled through a WordPress plugin interface.

5. Verification / Validation

Confirm the fix by attempting to access author archive pages without authentication.

• Post-fix check: Attempt to access https://example.com/author/testuser as an unauthenticated user; expect a 403 Forbidden error or redirect.
• Re-test: Repeat the curl command from section 3, and confirm it returns a 403 status code.
• Smoke test: Verify that logged-in users can still access their profiles and edit content normally.
• Monitoring: Check web server logs for blocked requests to author archive pages; this indicates the protection is working (example query).

curl -I https://example.com/author/testuser # Expected output: HTTP/1.1 403 Forbidden

6. Preventive Measures and Monitoring

Update security baselines to include user enumeration protection, and use automated scanning tools.

• Baselines: Update your WordPress security baseline to require a plugin with user enumeration protection.
• Asset and patch process: Review plugins regularly for updates, as they often contain security fixes.

7. Risks, Side Effects, and Roll Back

Installing a new plugin can sometimes cause compatibility issues.

• Risk or side effect 1: Plugin conflicts – some plugins may not be compatible with your existing WordPress setup; test in a staging environment first.
• Roll back: Deactivate the security plugin to revert to the previous state. Restore from backup if necessary.

8. References and Resources

• Vendor advisory or bulletin: https://hackertarget.com/wordpress-user-enumeration/
• NVD or CVE entry: No specific CVE currently exists for this vulnerability.
• Product or platform documentation relevant to the fix: https://wordpress.org/plugins/ (for plugin installation and configuration).