The Welcart e-Commerce plugin for WordPress is vulnerable to Insecure Direct Object Reference in all versions up to, and including, 2.12.5 via the 'member[ID]' parameter due to missing validation on a user controlled key. This makes it possible for unauthenticated attackers to overwrite any existing Welcart shop-member account's email address and password by supplying that member's numeric ID, then authenticate as that member to achieve full account takeover. The only authentication barrier is a wp_verify_nonce() check against a nonce printed to every unauthenticated visitor on the auto-published New Enrollment Form, meaning no existing account, no WordPress login, and no non-default configuration is required to exploit this vulnerability.
https://plugins.trac.wordpress.org/changeset/3760784/usc-e-shop/trunk/classes/usceshop.class.php
https://plugins.trac.wordpress.org/changeset/3760784/usc-e-shop
https://plugins.trac.wordpress.org/browser/usc-e-shop/tags/2.12.5/classes/usceshop.class.php#L5509
https://plugins.trac.wordpress.org/browser/usc-e-shop/tags/2.12.5/classes/usceshop.class.php#L5070
https://plugins.trac.wordpress.org/browser/usc-e-shop/tags/2.12.5/classes/usceshop.class.php#L4470
https://plugins.trac.wordpress.org/browser/usc-e-shop/tags/2.12.5/classes/usceshop.class.php#L3848