Custom Kohana_Exception class for handling exceptions in production.

error.php

<?php defined('SYSPATH') OR die('No direct access allowed!');

class Controller_Error extends Controller_Layout {

	public function before()
	{
		parent::before();

		$this->response->status((int) $this->request->action());

		$this->response->body(View::factory('erros/default', array(
			'page' => URL::site(rawurldecode(Request::$initial->uri())),
			'message' => base64_decode($this->request->param('message'))
		));
	}
}

exception.php

<?php defined('SYSPATH') OR die('No direct script access.');

/**
 * Custom exception class. If not in development environment shows a nice message with the error controller.
 * Logs all of the error information in the logs.
 *
 * @category   Exceptions
 * @author     Haralan Dobrev
 */
class Kohana_Exception extends Kohana_Kohana_Exception {

	public static function handler(Exception $e)
	{
		if (Kohana::DEVELOPMENT === Kohana::$environment)
		{
			// Shows the default red kohana error page with trace if we are in development
			parent::handler($e);
		}
		else
		{
			// Create a text version of the exception
			$error = Kohana_Exception::text($e);

			// Add this exception to the log
			Kohana::$log->add(Log::ERROR, $error);

			// Get the whole trace as a string
			$strace = Kohana_Exception::text($e) . "\n--\n" . $e->getTraceAsString();

			// Log that trace string with Log::STRACE level
			Kohana::$log->add(Log::STRACE, $strace);

			try
			{
				$attributes = array
					(
					// Every response code could have an action in the error controller
					// Use the 500 HTTP response code by default
					'action' => 500,
					
					// Don't show even the message if it's an internal error
					'message' => 'Something went wrong'
				);

				// Sets the action to the appropriate response code if it's an HTTP_Exception
				if ($e instanceof HTTP_Exception)
				{
					// Use the response code from the exception of it's an HTTP_Exception
					$attributes['action'] = $e->getCode();

					// Get the message from the exception
					$attributes['message'] = $e->getMessage();
				}

				// Encodes the message so there are no problems matching the route
				$attributes['message'] = base64_encode($attributes['message']);

				// Error sub-request using the error controller
				echo Request::factory(Route::get('error')->uri($attributes))
						->execute()
						->send_headers()
						->body();
			}
			catch (Exception $e)
			{
				// Clean the output buffer if one exists
				ob_get_level() and ob_clean();

				// Display the exception text
				echo $error;

				// Exit with an error status
				exit(1);
			}
		}
	}

}

Place the exception class in APPPATH/classes/kohana/exception.php

Add a route named 'error' with a message parameter. Like this:

Route::set('error', 'error/<action>(/<message>)')
    ->defaults(array(
        'controller' => 'error',
        'message' => ''
    ));

Add actions to the error controller with names of response codes like 403, 404, 500 and others.