Dev error stack trace leaking into prod in Play Framework

Play Framework is a web framework for Java and Scala. Verions prior to 2.8.16 are vulnerable to generation of error messages containing sensitive information. Play Framework, when run in dev mode, shows verbose errors for easy debugging, including an exception stack trace. Play does this by configuring its DefaultHttpErrorHandler to do so based on the application mode. In its Scala API Play also provides a static object DefaultHttpErrorHandler that is configured to always show verbose errors. This is used as a default value in some Play APIs, so it is possible to inadvertently use this version in production. It is also possible to improperly configure the DefaultHttpErrorHandler object instance as the injected error handler. Both of these situations could result in verbose errors displaying to users in a production application, which could expose sensitive information from the application. In particular, the constructor for CORSFilter and apply method for CORSActionBuilder use the static object DefaultHttpErrorHandler as a default value. This is patched in Play Framework 2.8.16. The DefaultHttpErrorHandler object has been changed to use the prod-mode behavior, and DevHttpErrorHandler has been introduced for the dev-mode behavior. A workaround is available. When constructing a CORSFilter or CORSActionBuilder, ensure that a properly-configured error handler is passed. Generally this should be done by using the HttpErrorHandler instance provided through d…