A Server Side Request Forgery vulnerability exists in the install app process in Sandstorm before build 0.203. A remote attacker may exploit this issue by providing a URL. It could bypass access control such as firewalls that prevent the attackers from accessing the URLs directly.
https://sandstorm.io/news/2017-03-02-security-review
https://github.com/sandstorm-io/sandstorm/commit/164997fb958effbc90c5328c166706280a84aaa1
https://devco.re/blog/2018/01/26/Sandstorm-Security-Review-CVE-2017-6200-en/