Groundhogg <= 4.9 - Authenticated (Sales Person+) Privilege Escalation via Contact Identity Rebinding leading to Administrator Account Takeover to 'user_id' Parameter (v3 /contacts) chained with v4 /emails/test

The Groundhogg — CRM, Newsletters, and Marketing Automation plugin for WordPress is vulnerable to Privilege Escalation via Contact Identity Rebinding in all versions up to, and including, 4.9 The vulnerability exists because the create_contact function in the v3 REST endpoint (POST /gh/v3/contacts) is gated solely by the add_contacts capability and forwards the full request payload — including the security-bearing user_id column — into the upsert path of Contacts_DB::add(), which bypasses the ownership guard that Contacts_DB::update() enforces, allowing an attacker to rebind any existing contact record to an arbitrary WordPress user ID. This makes it possible for authenticated attackers with Sales Representative-level access and above to upsert their own contact row to point to an Administrator's user ID, then invoke the v4 email-test endpoint (POST /gh/v4/emails/test) — also accessible to the Sales Representative role via the send_emails capability — to generate an {auto_login_url} one-time permissions key bound to the rebound contact, and consume that link to call wp_set_auth_cookie() and gain a fully authenticated session as the WordPress Administrator.