Timing Attack in Grav CMS CSRF Nonce Validation

Executive Summary

Grav CMS before 2.0.16 has a timing vulnerability in Utils::verifyNonce() where it uses a non-constant-time string comparison (=== operator) instead of hash_equals() for CSRF nonce validation. Attackers can exploit timing differences in responses to recover valid nonce values byte-by-byte through multiple requests, weakening CSRF protection.

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Detection Guidance

Check Grav CMS version with: grep -r 'version' /path/to/grav/vendor/getgrav/grav/composer.json. If version is below 2.0.16, the system is vulnerable. Monitor HTTP response times for nonce validation endpoints for unusual timing patterns that may indicate exploitation attempts.

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Impact Analysis

An attacker could bypass CSRF protections by recovering valid nonce values through timing attacks. This could allow unauthorized actions to be performed on behalf of authenticated users, such as changing account settings or making unintended changes to the site.

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Compliance Impact

This vulnerability weakens CSRF protection by allowing attackers to recover valid nonce values through timing attacks. While not directly violating GDPR or HIPAA, it could indirectly impact compliance by reducing the effectiveness of security controls designed to prevent unauthorized data access or modifications. Organizations using vulnerable Grav CMS versions may need to implement compensating controls or update systems to maintain compliance.

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Mitigation Strategies

Upgrade Grav CMS to version 2.0.16 or later immediately. If upgrading is not possible, modify the Utils::verifyNonce() function to use hash_equals() instead of === for nonce comparison. Review and harden CSRF protection mechanisms in the application.

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