[RDoc] XSS in project README files

Hi, While experimenting with parser bypass techniques, I discovered that RDoc markup could be used to inject a stored JavaScript payload into a project `README.rdoc` file. Please note that this issue is separate to my earlier report #200565 (XSS with AsciiDoc markup), marked as duplicate. ## Steps to Reproduce 1. Create a new GitLab project 2. Initialise the project by creating a `README` file 3. Set the file title to `README.rdoc` 4. Paste the below Payload into the file 5. Commit the file to the project and click on the "XSS" link ## Proof of Concept Payload `XSS[JaVaScriPt:alert(1)] <-- click to test` Thanks!