Open registration on a test copy of Gitlab

HackerOne report #744935 by iframe on 2019-11-23, assigned to @cmaxim:

Hi, I found a subdomain on which there is a test copy of gitlab, I saw that registration is open there and successfully registered there, this copy is fresh so I think that tests will be carried out there.

https://mr-sidebar.prototype.gitlab.com/

https://mr-sidebar.prototype.gitlab.com/test1337

Impact

Open registration on a test copy of Gitlab