Most plugins like exec-php are now deprecated and not updated anymore.
And the solution to the problem is extremely simple.

To enable the PHP in your widgets simply open the functions.php of your theme
and paste this code before a closing anchor.

// PHP in Widgets
add_filter('widget_text','execute_php',100);
function execute_php($html){
if(strpos($html,"<"."?php")!==false){ ob_start(); eval("?".">".$html);
$html=ob_get_contents();
ob_end_clean();
}
return $html;
}