In WordPress before 4.7.5, there is a lack of capability checks for post meta data in the XML-RPC API.
https://wpvulndb.com/vulnerabilities/8817
https://wordpress.org/news/2017/05/wordpress-4-7-5/
https://github.com/WordPress/WordPress/commit/e88a48a066ab2200ce3091b131d43e2fab2460a4
https://codex.wordpress.org/Version_4.7.5
http://www.securitytracker.com/id/1038520