Events Manager - Calendar, Bookings, Tickets, and more! < 7.3.4 - Unauthenticated Stored Cross-Site Scripting via Event Attributes

Description

The Events Manager - Calendar, Bookings, Tickets, and more! plugin for WordPress is vulnerable to Stored Cross-Site Scripting via event attribute values in all versions up to, and including, 7.3.3. This is due to insufficient input sanitization when storing attribute values (using only `wp_unslash()` without sanitization) and lack of output escaping when rendering the '#_ATT{key}' placeholder. This makes it possible for authenticated attackers, with Author-level access and above, or unauthenticated attackers when anonymous event submissions are enabled, to inject arbitrary web scripts that execute when any user views the affected event page.