Zer0SumGam3/CVE-2026-66066-POC ? reverse-engineered prompt

Build me a small local lab that reproduces this Rails Active Storage and libvips issue end to end.

I want a Docker based Rails app that looks like a normal upload feature, with a page to create an upload, a show page that displays the image variant, and a simple controller and model for a single attached image. Then add a Python script that can build the special upload file, send it through the normal app flow, and trigger the vulnerable image processing behavior against a local target only. It should also support an optional callback URL so I can confirm when the payload runs.

Please keep it self contained, run only on localhost, and make the target as close to a stock Rails app as possible. If you need to check current Rails or libvips details while wiring it up, look them up online. Also include a simple way to build and run the lab with Docker and to test the patched version afterward.