In PHP Proxy 3.0.3, any user can read files from the server without authentication due to an index.php?q=file:/// LFI URI, a different vulnerability than CVE-2018-19246.
PHP-Proxy 5.1.0 allows remote attackers to read local files if the default "pre-installed version" (intended for users who lack shell access to their web server) is used.
The str_rot_pass function in vendor/atholn1600/php-proxy/src/helpers.php in PHP-Proxy 5.1.0 uses weak cryptography, which makes it easier for attackers to calculate the authorization data needed for local file inclusion.
THREATIST.IORead the docs