Billing control is security, to be clear, but beyond that: The key permissions that enable anyone to generate text also grant access to all GCP Generative AI endpoints in the project they were provisioned in. That includes things like Files that your system might have uploaded to Gemini for processing, and querying the Gemini context caches for recent Gemini completions your system did. Both of these are likely to contain customer-facing data, if your organization & systems use them.
If you're hearing this and your gut reaction is This can't be real; We're on the same page. Its a staggering issue that Google has categorically failed to respond to. They automatically added this permission to existing keys that they knew their customers were publishing publicly on the internet, because the keys are legitimately supposed to be public for things like client-side Firebase access & Google Maps tile rendering.
They did not notify customers that they were doing this. They did not notify customers after this issue was reported to them months later by Truffle. They did not automatically remove the additional key grants for customers. They continue to push guidance targeted at novices like "just put the Gemini key behind a proxy (that's also publicly exposed on the internet)", which might solve the unintentional files and caching endpoint leaks but doesn't solve the billing issue. They denied that Truffle's initial report was even valid, until Truffle used the Internet Archive to find a Google internal key from 2023, published for a Google Maps widget or something, before Gemini was even released, that was still active, and used it to demonstrate to Google that, hey, anyone can use this key to get Gemini completions on the house, is there anyone driving this ship??" Google fixed the permissions on that specific key. And did nothing else.