The Formidable Forms plugin for WordPress is vulnerable to an authorization bypass through user-controlled key in all versions up to, and including, 6.28. This is due to the frm_strp_amount AJAX handler (update_intent_ajax) overwriting the global $_POST data with attacker-controlled JSON input and then using those values to recalculate payment amounts via field shortcode resolution in generate_false_entry(). The handler relies on a nonce that is publicly exposed in the pages JavaScript (frm_stripe_vars.nonce), which provides CSRF protection but not authorization. This makes it possible for unauthenticated attackers to manipulate PaymentIntent amounts before payment completion on forms using dynamic pricing with field shortcodes, effectively paying a reduced amount for goods or services.
Weakness
The system’s authorization functionality does not prevent one user from gaining access to another user’s data or record by modifying the key value identifying the data.
Extended Description
Retrieval of a user record occurs in the system based on some key value that is under user control. The key would typically identify a user-related record stored in the system and would be used to lookup that record for presentation to the user. It is likely that an attacker would have to be an authenticated user in the system. However, the authorization process would not properly check the data access operation to ensure that the authenticated user performing the operation has sufficient entitlements to perform the requested data access, hence bypassing any other authorization checks present in the system. For example, attackers can look at places where user specific data is retrieved (e.g. search screens) and determine whether the key for the item being looked up is controllable externally. The key may be a hidden field in the HTML form field, might be passed as a URL parameter or as an unencrypted cookie variable, then in each of these cases it will be possible to tamper with the key value. One manifestation of this weakness is when a system uses sequential or otherwise easily-guessable session IDs that would allow one user to easily switch to another user’s session and read/modify their data.
Potential Mitigations
References
- https://plugins.trac.wordpress.org/browser/formidable/tags/6.28/stripe/controllers/FrmStrpLiteHooksController.php#L88
- https://plugins.trac.wordpress.org/browser/formidable/tags/6.28/stripe/models/FrmStrpLiteAuth.php#L322
- https://plugins.trac.wordpress.org/browser/formidable/tags/6.28/stripe/models/FrmStrpLiteAuth.php#L402
- https://plugins.trac.wordpress.org/changeset?sfp_email=\u0026sfph_mail=\u0026reponame=\u0026new=3480574%40formidable%2Ftrunk\u0026old=3460198%40formidable%2Ftrunk\u0026sfp_email=\u0026sfph_mail=
- https://www.wordfence.com/threat-intel/vulnerabilities/id/b8be3b6e-a035-4e6f-ba2b-ce9e59ebf2e0?source=cve