The vulnerability stems from the User model's $hidden array configuration in 'src/MicroweberPackages/User/Models/User.php' not including sensitive fields (e.g., 'two_factor_secret', 'oauth_uid') prior to version 1.3.4. This caused these fields to be exposed during serialization (e.g., via toArray() or toJson()). However, the exposure is due to a misconfiguration in the model's property, not a specific custom function. The patch adds these fields to the $hidden array, resolving the issue. Since the vulnerability arises from framework-level serialization behavior rather than explicit functions in the codebase, no specific functions are identified as vulnerable with high confidence.