Page and Post Clone <= 6.3 - Authenticated (Contributor+) SQL Injection via 'meta_key' Parameter

The Page and Post Clone plugin for WordPress is vulnerable to SQL Injection via the 'meta_key' parameter in the content_clone() function in all versions up to, and including, 6.3. This is due to insufficient escaping on the user-supplied meta_key value and insufficient preparation on the existing SQL query. This makes it possible for authenticated attackers, with Contributor-level access and above, to append additional SQL queries into already existing queries that can be used to extract sensitive information from the database. The injection is second-order: the malicious payload is stored as a post meta key and executed when the post is cloned.