With a valid key, an attacker can access uploaded files, cached data, and charge LLM-usage to your account. The keys now also authenticate to Gemini even though they were never intended for it. The problem occurs when users enable the Gemini API on a Google Cloud project, causing existing API keys to gain surreptitious access to Gemini endpoints without any warning or notice.
For more than a decade, Google's developer documentation has described these keys, identified by the prefix 'Aiza', as a mechanism used to identify a project for billing purposes. Developers generated a key and then pasted it into their client-side HTML code in full public view.