Solution for “A Weird XSS Case”

A detailed analysis of a cross-site scripting (XSS) challenge on the BSidesDublin 2019 site: the author reviews the JavaScript input validation, finds bypasses using non-ASCII characters that map to ASCII through case conversions, crafts payloads to manipulate the DOM and invoke JavaScript without lowercase letters, and demonstrates working exploit payloads (including a Function-constructor and pseudo-URL techniques). The write-up includes code excerpts, the logic of the filters, and multiple successful bypasses and proofs of concept.