The MailOptin – Popup, Optin Forms & Email Newsletters for Mailchimp, HubSpot, AWeber Etc

Why it is Amber

• CVSS 9.8 critical
• Remotely exploitable without logging in

References

• https://plugins.trac.wordpress.org/browser/mailoptin/tags/1.2.78.5/src/connections/WordPressUserRegistrationConnect/Subscription.php#L68
• https://plugins.trac.wordpress.org/browser/mailoptin/tags/1.2.78.5/src/core/src/AjaxHandler.php#L699
• https://plugins.trac.wordpress.org/browser/mailoptin/tags/1.2.78.5/src/core/src/Connections/AbstractConnect.php#L84
• https://plugins.trac.wordpress.org/changeset/3744644/mailoptin/trunk/src/connections/WordPressUserRegistrationConnect/Subscription.php
• https://plugins.trac.wordpress.org/changeset?reponame=&new=3744644%40mailoptin%2Ftrunk&old=3738326%40mailoptin%2Ftrunk#file4
• https://www.wordfence.com/threat-intel/vulnerabilities/id/96111116-6b6f-42fc-98d8-6f5c27dc3c1c?source=cve

Original description

The MailOptin – Popup, Optin Forms & Email Newsletters for Mailchimp, HubSpot, AWeber Etc. plugin for WordPress is vulnerable to Privilege Escalation in all versions up to, and including, 1.2.78.6 This is due to the `subscribe_to_email_list` endpoint accepting an attacker-supplied `optin_data[form_custom_field_mappings]` parameter without any allow-list validation on destination keys, allowing the attacker-controlled mapping to override the administrator's saved mapping and pass arbitrary `wp_users` column names — including `ID` and `user_pass` — directly into `wp_insert_user()` via the `subscribe()` function. This makes it possible for unauthenticated attackers to force `wp_insert_user()` into UPDATE mode on any existing account by supplying a target user's numeric `ID`, overwrite that account's password with a pre-hashed value of their choosing, and thereby take over any WordPress user account — including administrators — leading to full site compromise. Exploitation requires that a WordPress User Registration opt-in form is published somewhere on the site, though the form's UUID is visible in page source and no authentication, nonce, or capability check is required to reach the vulnerable endpoint.