Discourse's SSRF protection missing for some FastImage requests

Discourse is an open-source discussion platform. Prior to version 3.1.0.beta3 of the beta and tests-passed branches, some user provided URLs were being passed to FastImage without SSRF protection. Insufficient protections could enable attackers to trigger outbound network connections from the Discourse server to private IP addresses. This affects any site running the tests-passed or beta branches versions 3.1.0.beta2 and prior. This issue is patched in version 3.1.0.beta3 of the beta and tests-passed branches. There are no known workarounds.