PHP <=5.3 – preg_match() full path disclosure

 

PHP <=5.3 – preg_match() full path disclosure

[MajorSecurity Advisory #57]PHP <=5.3 – preg_match() full path disclosure

Details

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Product: PHP <=5.3

Security-Risk: moderated

Remote-Exploit: yes

Vendor-URL: http://www.php.net/
Vendor-Status: informed

Advisory-Status: published

Credits

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Discovered by: David Vieira-Kurz
http://www.majorsecurity.info
Affected Products:

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PHP 5.3 and prior

PHP 5.2.11 and prior

Original Advisory:

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http://www.majorsecurity.info/index_2.php?major_rls=major_rls57
Introduction

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“PHP is a widely-used general-purpose scripting language that is

especially suited for Web development and can be embedded into HTML.”

- from php.net

More Details

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1. Full Path Disclosure

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There is a full path disclosure vulnerability concerning the

preg_match() php function which allow attackers to

gather the real path of the server side script.

The preg_match() PHP function takes strings as parameters and will raise

warnings when values that are passed are arrays rather then strings.

To get the path of the current script, you simply need to pass the

arguments as arrays rather then expected strings

and then simply read the warning message generated by PHP to see the

error including the full path of the current running script.

Proof of concept:
http://localhost/cms/modules/system/admin.php?fct=users&op[]=
Warning: preg_match() expects parameter 2 to be string, array given in

/htdocs/cms/include/common.php on line 105

Solution

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I would NOT recommend to just react by “security through obscurity” and

turn off the error messages, error reporting etc.

This is not a solution because there are a lot of users that are having

a shared hosting server where they aren’t able to manipulate

the “php.ini” configuration file – even ini_set() is forbidden on some

shared hoster servers.

So they still would have the full path disclosure there.

Workaround

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I would recommend to meticulously go through the code forcing PHP to

cast the data to the desired type, in this case the (string) casts

to eliminate the Notice or Warning messages.

Example:

<?PHP

if(isset($_GET['page'])) {

if (is_array($page = $_GET['page'])) {

$casted = (string)$page;

} else {

$page = htmlspecialchars($_GET['page'],ENT_QUOTES,’UTF-8′);

validate_alpha($page);

}

}

function validate_alpha($page) {

return preg_match(”/^[A-Za-z0-9_-]+$/ “, $page);

} ?>

Vendor communication

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The PHP Developer team has been informed that there is this vulnerability.

MajorSecurity

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MajorSecurity is a German penetrationtesting and security research

company which focuses on web application security. We offer professional

penetrationtestings, security audits,

source code reviews and reliable proof of concepts.

You will find more Information about MajorSecurity at
http://www.majorsecurity.info/