PHP 5.3 - 'preg_match()' Full Path Disclosure








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

Product: PHP <=5.3
Security-Risk: moderated
Remote-Exploit: yes
Vendor-Status: informed
Advisory-Status: published

Discovered by: David Vieira-Kurz

Affected Products:
PHP 5.3 and prior
PHP 5.2.11 and prior

Original Advisory:

"PHP is a widely-used general-purpose scripting language that is 
especially suited for Web development and can be embedded into HTML."
- from

More Details
1. Full Path Disclosure
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:

Warning: preg_match() expects parameter 2 to be string, array given in 
/htdocs/cms/include/common.php on line 105

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.

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.

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

$casted = (string)$page;
} else {
$page = htmlspecialchars($_GET['page'],ENT_QUOTES,'UTF-8');
function validate_alpha($page) {
return preg_match("/^[A-Za-z0-9_-]+$/ ", $page);
} ?>

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

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