Groundhogg <= 4.9 - Authenticated (Custom+) Privilege Escalation to 'user' Parameter

The Groundhogg — CRM, Newsletters, and Marketing Automation plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 4.9 This is due to a missing ownership and capability check on the user parameter within the process_edit() function, which allows any authenticated user with the edit_contacts capability to reassign a contact record's linked WordPress user ID to any arbitrary account without requiring the edit_users or promote_users capabilities. This makes it possible for authenticated attackers, with sales_rep-level access and above, to escalate their privileges to administrator by linking a contact to an administrator's WordPress user ID, then creating a note containing the {auto_login_link} replacement tag to trigger generation of a valid auto-login permissions-key URL for the administrator-linked contact, and finally visiting that URL to authenticate as the targeted administrator. The auto-login URL is stored in the note content and is readable back by the attacker via the view_notes and add_notes capabilities that the sales_rep role holds by default.