Letting an uncaught exception error reach the user is generally bad. It risks exposing secrets / confidential information to the user and any returned client side secrets risk getting into intermediary caches. The biggest risk is the user input being returned in the response creating an XSS (cross site scripting) risk. This is a very common source of reflected XSS vulnerabilities. You should always catch exceptions like this so you can at the very least sanitize them for XSS. This is already built in to some frameworks. If you are using something that doesn't you need to do it yourself and it's probably easier to just strip it all in production, you just need to make sure you are still setting an appropriate status code.