Email Address Enumeration in Grav Login Plugin

Executive Summary

The Grav Login plugin before version 3.9.1 has a flaw in its registration process that allows attackers to determine which email addresses are already registered on a site. When someone tries to register with an email that exists, the system shows a specific error message, but registration proceeds normally for non-existent emails. Since there is no rate limiting, attackers can repeatedly submit registration attempts to enumerate valid email addresses.

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Detection Guidance

To detect this vulnerability, monitor the Grav Login plugin registration endpoint for repeated attempts with different email addresses. Check for distinct error responses like 'EMAIL_NOT_AVAILABLE' when an email exists versus silent success for non-existent emails. Use tools like curl to test registration endpoints with various email addresses and observe responses.

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Impact Analysis

This vulnerability allows attackers to identify valid email addresses on your site, which can lead to targeted phishing attacks, credential stuffing, or social engineering attempts. It compromises user privacy by exposing which accounts exist and may facilitate further attacks against those accounts.

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Compliance Impact

This vulnerability may violate privacy regulations like GDPR by exposing personal data (email addresses) without consent. It could also breach HIPAA if used to identify accounts in healthcare systems, potentially compromising protected health information. Organizations may face compliance penalties for failing to protect user data.

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Mitigation Strategies

Immediately update the Grav Login plugin to version 3.9.1 or later. Implement rate limiting on the registration endpoint to prevent brute-force enumeration attempts. Modify error handling to return generic messages regardless of email existence to avoid leaking account information.

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