Fix #yogosha4534

htdocs/core/lib/functions.lib.php

@@ -606,9 +606,9 @@ function GETPOST($paramname, $check = 'alphanohtml', $method = 0, $filter = null
 			break;
 	}
 
-	// Sanitizing for special var name. There is no reason to allow a backtopage to an external URL.
+	// Sanitizing for special parameters. There is no reason to allow the backtopage parameter to contains an external URL.
 	if ($paramname == 'backtopage') {
-		$out = preg_replace(array('/\/\/+/', '/^[a-z]*:/'), '', $out);
+		$out = preg_replace(array('/[\\\/][\\\/]+/', '/^[a-z]*:/'), '', $out);
 	}
 
 	// Code for search criteria persistence.