[txcwpalpha]

>That said, I don't blame Twilio for not catching this

I do.

Twilio is a multi-billion dollar company and there is no excuse for them not having proper security processes to catch stuff like this early. Even if we take the "S3 is hard" arguments at face value, this wasn't a 0-day or some complicated unpredictable exploit. This was an extremely basic misconfiguration on a mission-critical part of their architecture that would have been caught by even the simplest out-of-the-box penetration test or audit. For a company like Twilio to not be doing basic, fundamental stuff like that is a big deal and they certainly should be blamed for it.