PHP escapeshellarg Windows Vulnerability

[Daniel Fabian]

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


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DESCRIPTION
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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:



$user =3D escapeshellarg($_GET['user']);
$pwd =3D escapeshellarg($_GET['pwd']);

system("htpasswd -nb $user $pwd", $return);


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


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GENERAL REMARKS
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- 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).

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Recommended Hotfixes
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Update PHP to version 4.3.7.


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

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Contact
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