PYSEC-2026-3693 Pydantic AI: Unvalidated UploadedFile references in UI adapters allow server-side file access using the application's credentials

Summary A client that can submit message history to a Pydantic AI UI adapter can reference arbitrary files in the application's model-provider or cloud-storage account. The server forwards the reference to the model provider, which fetches it using the server's own credentials, allowing the clien...