The MasterStudy LMS WordPress Plugin WordPress plugin before 3.7.50 does not check whether user registration is enabled on the site before creating an account through one of its front-end registration flows, allowing unauthenticated users to create accounts, and be logged into them, on sites where registration has been deliberately disabled.
https://wpscan.com/vulnerability/57b0dd3f-bd83-4fb7-b98d-c999026910cd/