Summary:
Ref T6755. Although we do not return response bodies, it is possible to perform crude portscanning if you can execute a DNS rebinding attack (which, for now, remains theoretical).
Limit users to 60 requests / hour to make it less feasible. This would require ~30 years to portscan all ports on a `/32` netblock.
Users who can guess that services may exist can confirm their existence more quickly than this, but if the attacker already had a very small set of candidate services it seems unlikely that portscanning would be of much use in executing the attack.
This protection should eventually be applied to T4190, too (that task also has other considerations).
Test Plan: Set rate limit very low, hit rate limit.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T6755
Differential Revision: https://secure.phabricator.com/D12168
