How to remediate – CraftCMS User Enumeration

1. Introduction

CraftCMS User Enumeration allows attackers to identify valid usernames on a CraftCMS installation. This information can be used in brute-force attacks against the login page, potentially gaining unauthorized access. Affected systems are typically publicly accessible CraftCMS websites running default configurations. A successful exploit could compromise confidentiality through account takeover and impact integrity if accounts have administrative privileges.

2. Technical Explanation

• Root cause: Lack of access control restrictions on user information retrieval endpoints.
• Exploit mechanism: An attacker sends requests to ‘/index.php?p=admin%2Factions%2Fusers%2Fsend-password-reset-email’ with different usernames to identify valid accounts.
• Scope: CraftCMS installations, particularly those using default configurations.

3. Detection and Assessment

To confirm vulnerability, check if the user enumeration endpoint is accessible. A thorough method involves attempting to request password reset emails for various usernames.

• Quick checks: Check the CraftCMS version in the admin panel (Settings -> General). Older versions are more likely to be affected.
• Scanning: Nessus plugin 16843, or other vulnerability scanners with CraftCMS-specific plugins may identify this issue. These should be considered examples only.
• Logs and evidence: Examine web server logs for requests to ‘/index.php?p=admin%2Factions%2Fusers%2Fsend-password-reset-email’. Frequent requests with varying usernames indicate potential enumeration attempts.

curl -I https://yourcraftcmssite.com/index.php?p=admin%2Factions%2Fusers%2Fsend-password-reset-email

4. Solution / Remediation Steps

Block requests to the sensitive user information endpoint at the server level. This can be achieved using .htaccess or a Web Application Firewall (WAF).

4.1 Preparation

• No services need to be stopped for this remediation.
• Roll back plan: Remove the .htaccess rule or WAF configuration if issues arise.

4.2 Implementation

1. Step 1: Add a rule to your .htaccess file to block access to ‘/index.php?p=admin%2Factions%2Fusers%2Fsend-password-reset-email’.
2. Step 2: If using a WAF, configure it to block requests matching the same URL pattern.

4.3 Config or Code Example

Before

# No specific rule blocking user enumeration endpoint

After

<Location /index.php?p=admin%2Factions%2Fusers%2Fsend-password-reset-email>
  Order Allow,Deny
  Deny from all
</Location>

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent this issue. Least privilege reduces the impact of compromised accounts. Input validation prevents malicious data from being processed. Secure configuration ensures default settings do not expose sensitive information.

• Practice 1: Implement least privilege for CraftCMS users, limiting access to only necessary functions.
• Practice 2: Regularly review and update CraftCMS configurations to ensure secure defaults are in place.

4.5 Automation (Optional)

Automation is not directly applicable for this specific remediation step without a configuration management tool.

5. Verification / Validation

Confirm the fix by attempting to access the blocked endpoint and verifying that it returns an error. Re-test using the earlier detection method to confirm the issue is resolved.

• Post-fix check: Attempting to access https://yourcraftcmssite.com/index.php?p=admin%2Factions%2Fusers%2Fsend-password-reset-email should return a 403 Forbidden error.
• Re-test: Repeat the curl command from the detection phase; it should now return a 403 status code.
• Monitoring: Monitor web server logs for any attempts to access the blocked endpoint, indicating potential malicious activity.

curl -I https://yourcraftcmssite.com/index.php?p=admin%2Factions%2Fusers%2Fsend-password-reset-email

6. Preventive Measures and Monitoring

Regular security baselines, including checks for default configurations, can prevent this issue. Incorporating SAST or DAST tools into CI/CD pipelines helps identify vulnerabilities early in the development process. A regular patch review cycle ensures timely application of security updates.

• Baselines: Update your CraftCMS security baseline to include a check for access control restrictions on user information endpoints.
• Pipelines: Add SAST or DAST tools to your CI/CD pipeline to scan for vulnerabilities in CraftCMS code and configurations.
• Asset and patch process: Implement a regular patch review cycle (e.g., weekly) to ensure timely application of security updates.

7. Risks, Side Effects, and Roll Back

Blocking the endpoint may inadvertently block legitimate password reset functionality if custom modifications have been made. The roll back steps involve removing the .htaccess rule or WAF configuration.

• Risk or side effect 1: Blocking the endpoint could interfere with custom password reset workflows.
• Roll back: Remove the added <Location> block from your .htaccess file, or disable the corresponding WAF rule.

8. References and Resources

• Vendor advisory or bulletin: https://craftcms.com/knowledge-base/securing-craft