GHSA-j8g8-j7fc-43v6: Flowise has Arbitrary File Upload via MIME Spoofing

Flowise has a file upload vulnerability where the server only checks the `Content-Type` header (MIME type spoofing, pretending a file is one type when it's actually another) that users provide, instead of verifying what the file actually contains. Because the upload endpoint is whitelisted (allowed without authentication), an attacker can upload malicious files by claiming they're safe types like PDFs, leading to stored attacks or remote code execution (RCE, where attackers run commands on the server).