Impact

This vulnerability may allow SameSite Attackers to bypass the CodeIgniter4 CSRF protection mechanism with CodeIgniter Shield.

For this attack to succeed, the attacker must have direct (or indirect, e.g., XSS) control over a subdomain site (e.g., https://a.example.com/) of the target site (e.g., http://example.com/).

This vulnerability exists whether Config\Security::$csrfProtection is 'cookie' or 'session'.
It is also exploitable whether Config\Security::$regenerate is true or false.

Patches

Upgrade to CodeIgniter v4.2.3 or later and Shield v1.0.0-beta.2 or later.

Workarounds

Do all of the following:

• set Config\Security::$csrfProtection to 'session'
• remove old session data right after login (immediately after ID and password match)
• regenerate CSRF token right after login (immediately after ID and password match)

References

• CodeIgniter4 CSRF Protection
• SameSite Attacks
• SameSite Cookies
• The great SameSite confusion

For more information

If you have any questions or comments about this advisory:

• Open an issue or discussion in codeigniter4/shield
• Email us at security@codeigniter.com