Import and export users and customers <= 2.0.8 - Authenticated (Subscriber+) Privilege Escalation via Multisite Capability Meta Fields

The Import and export users and customers plugin for WordPress is vulnerable to Privilege Escalation in all versions up to and including 2.0.8 via the `save_extra_user_profile_fields()` function. This is due to an incomplete blocklist that correctly restricts capability meta keys for the primary site (e.g., `wp_capabilities`, `wp_user_level`) but fails to block the equivalent meta keys for any other subsite in a WordPress Multisite network (e.g., `wp_2_capabilities`, `wp_2_user_level`), allowing these keys to pass the `in_array()` check and be written directly to user meta via `update_user_meta()`. This makes it possible for authenticated attackers, with Subscriber-level access and above, to escalate their privileges to Administrator on any subsite within the Multisite network by submitting a crafted profile update to `/wp-admin/profile.php`. Exploitation requires that an administrator has previously imported a CSV file containing multisite-prefixed capability column headers and has enabled the 'Show fields in profile?' option, which causes those keys to be stored in the `acui_columns` option and exposed as editable fields on the user profile page.