GHSA-88pr-878c-24wf: Flowise: Authenticated arbitrary file write in the `S3 Directory` document loader via unsanitized S3 object keys

Flowise on current main allows an authenticated user with documentStores:preview-process permission to trigger the S3 Directory document loader with attacker-controlled S3 object keys. The loader joins each returned S3 key with a temporary directory using path.join(tempDir, key) and writes the object bytes to disk without validating traversal sequences such as ../. Cleanup later removes only the original temporary directory, so files written outside that directory persist on the host filesystem.

This yields arbitrary file write with the privileges of the Flowise server process.

A related variant exists in the S3File loader when fileProcessingMethod = unstructured (same root cause; its cleanup behavior turns it into a mixed arbitrary write/delete/DoS primitive).