Inefficient Regular Expression Complexity in gradio

Summary

A Regular Expression Denial of Service (ReDoS) vulnerability exists in the gradio-app/gradio, affecting the "gr.Datetime" component. The vulnerability arises from the use of a regular expression `^(?:\s*now\s*(?:-\s*(\d+)\s*([dmhs]))?)?\s*$` to process user input. In Python's default regex engine, this regular expression can take polynomial time to match certain crafted inputs. An attacker can exploit this by sending a crafted HTTP request, causing the gradio process to consume 100% CPU and potentially leading to a Denial of Service (DoS) condition on the server. This issue affects 4.38.0 and later.