Get Action and Action Parameters in Controller.OnException

protected override void OnException(ExceptionContext filterContext)
{
    string action = filterContext.RouteData.Values["action"].ToString();
    string controller = filterContext.RouteData.Values["controller"].ToString();
}

You can get all these data from ExceptionContext object.

For example using this code you can get controller, action and all other routing parameters:

context.RouteData.Values

Using this code you can get query string parameters:

context.HttpContext.Request.QueryString

And finnaly form parameters:

context.HttpContext.Request.Form