SEC-CONSULT Security Advisory - PHP: Hypertext Preprocessor

Vendor: PHP (http://www.php.net)
Product: PHP 4.3.6 and below (verified in 4.3.5 which was current when
the bug was discovered)
Vendor status: vendor contacted (04-04-2004)
Patch status: Problem fixed in 4.3.7

===========
DESCRIPTION
===========

PHP offers the function escapeshellarg() to escape arguments to shell
commands in a way that makes it impossible for an attacker to execute
additional commands. However due to a bug in the function, this does not
work with the windows version of PHP.

Vulnerable is for example the following code:

[code]
$user = escapeshellarg($_GET['user']);
$pwd = escapeshellarg($_GET['pwd']);

system("htpasswd -nb $user $pwd", $return);
[/code]

If an attacker enters '" || dir || ' (without the single quotes) for
user (or pwd), the command dir is executed.

===============
GENERAL REMARKS
===============

- The bug was successfully verified in PHP 4.3.3 and 4.3.5. In former
version (4.3.3) the execution of additional commands was only possible
when single quotes were used.

- While correcting the vulnerability, the PHP staff seems to have
noticed that the function escapeshellcmd is vulnerable too (according to
the changelog of v4.3.7).

====================
Recommended Hotfixes
====================

Update PHP to version 4.3.7.

EOF Daniel Fabian / @2004
d.fabian at sec-consult dot com

=======
Contact
=======

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A-1080 Wien
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Tel.: +43 / 1 / 409 0307 - 570
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