The Sitemap by click5 WordPress plugin before 1.0.36 does not have authorisation and CSRF checks when updating options via a REST endpoint, and does not ensure that the option to be updated belongs to the plugin. As a result, unauthenticated attackers could change arbitrary blog options, such as the users_can_register and default_role, allowing them to create a new admin account and take over the blog.
CWE-352, CWE-862