psx/sandbox

PHP sandbox to execute a safe subset of the PHP programming language

v0.2.0 2018-05-30 18:19 UTC

README

About

This library helps to execute PHP code which was provided by a user. I.e. if your app wants to provide a scripting feature where the user can provide custom PHP code. This library helps to parse this untrusted code and execute it only if there are safe calls.

Internally the library uses the PHPParser library to parse the code. To make the code safe the sandbox allows only a small subset of PHP. It is not possible to define a class, interface or trait. Also all functions which produce output i.e. echo, print, etc. are not allowed. The only way a user can return a value is by using the return statement in the script. Every function and new call gets checked by the security manager. The security manager contains a whitelist of all allowed functions and classes.

Its important to note that the security check is not performed on runtime, instead we simply prevent to generate PHP code which contains untrusted code. Because of this features like i.e. dynamic functions names $func = 'foo'; $func(); are also not allowed.

If the code is clean the runtime generates normal PHP code and writes this to a file. All subsequent calls simply include and execute this code, thus the sandbox has almost no performance loss.

Security

It is not recommended to run PHP code from anonymous users on the internet. This feature is intended to be used i.e. by customers of a SAAS solution which need to customize specific parts of the app. If you have found a way to breakout of the sandbox please open an issue or if you like you can also create a pull request with a fitting test case. Please take a look at the tests folder to see already covered cases.

Usage

<?php

$code = <<<'CODE'
<?php

return [
    'result' => $my_service,
];

CODE;

$runtime = new \PSX\Sandbox\Runtime('my_code');
$runtime->set('my_service', 'foo');
$response = $runtime->run($code);