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Re: CVE request: is_a() function may allow arbitrary code execution in PHP 5.3.7/5.3.8
From: Stas Malyshev <smalyshev () sugarcrm com>
Date: Sat, 24 Sep 2011 16:22:11 -0700

Hi!

On 9/24/11 6:56 AM, Vincent Danen wrote:
Could a CVE be assigned for this flaw?  PHP 5.3.7 changed how the is_a()
function worked, and as a result it could allow for remote arbitrary
code execution if certain specific conditions are met (the blog post
referenced below has a good writeup of the flaw).

I don't see what is to assign CVE to. Almost any function dealing with classes as strings (including new $foo operator) can result in autoloader call. If your autoloader is broken and your security practices are non-existant, this can cause remote code execution. Just as if you write in your script eval($_GET['hackme']), it can lead to remote code execution. It is not a flaw in PHP, _GET or eval() function - it is a flaw in how you use them. You should not be using them this way, and if you have autoloader that does includes, you should check what are you including and set allow_url_includes to Off.

http://www.byte.nl/blog/2011/09/23/security-bug-in-is_a-function-in-php-5-3-7-5-3-8/
https://bugs.php.net/bug.php?id=55475
https://bugzilla.redhat.com/show_bug.cgi?id=741020

It looks like this is the fix:

http://svn.php.net/viewvc/?view=revision&amp;revision=317183

This is not a "fix" - it is a reversal of BC break because it should not be introduced in 5.3 version. However, that does not fix broken autoloaders that accept any string as class name and try to load them. It removes one specific code path that people misusing one specific function were taking. If their autoloader is broken, they still can be in trouble in other ways, and they need to fix their code.
--
Stanislav Malyshev, Software Architect
SugarCRM: http://www.sugarcrm.com/
(408)454-6900 ext. 227


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