A stored Cross-Site Scripting (XSS) vulnerability exists in the contact detail view of Mautic 7. Values of HTML-type custom contact fields are rendered without output sanitization. A user or integration able to write a value to such a field (for example, through contact editing, the contact API, or a form submission mapped to the field) can store a script payload in it. When another user, including an administrator, opens the affected contact's detail page, the injected script executes within the context of their active browser session. This could allow an attacker to perform administrative actions on behalf of the victim, such as creating new administrator accounts, altering system configuration, or accessing contact and campaign data.
There are no official workarounds. To mitigate this vulnerability without upgrading, restrict contact create and edit permissions and API access to trusted users, and avoid mapping public form fields or publicly updatable settings to HTML-type contact fields.