PHP is a widely-used general-purpose scripting language that is
especially suited for Web development and can be embedded into HTML.
More information is available at http://www.php.net.
Remote exploitation of an input validation vulnerability in The PHP
Group's HTML-embedded scripting language PHP allows attackers to bypass
The problem specifically exists within the shell command escape routines
escapeshellcmd() and escapeshellarg(). These routines are intended for
escaping shell metacharacters that may be present in user-supplied data
prior to passing them to command execution routines such as system(),
passthru(), popen(), exec() or the backtick operator. While both filter
routines are functional on the Unix platform, they fail to filter all
characters on the Windows platform. The escapeshellcmd() routine fails
to filter the characters '%|>', allowing attackers to access environment
variables, redirect output and execute arbitrary commands. The
escapeshellarg() routine fails to filter the character '%', allowing an
attacker to access environment variables.
Exploitation allows attackers to compromise an affected system under the
web server's privileges. Systems are not vulnerable by default, as a
publicly accessible script must be present that utilizes one of the
affected routines with user-supplied data.
iDEFENSE has confirmed the existence of this vulnerability in PHP
version 4.3.6 running on Microsoft Windows platforms. It is suspected
that previous versions are also vulnerable.
Pass user-supplied data through custom character filters implemented
with str_replace() or preg_replace(). Example:
$user_supplied = preg_replace("/[>|%]/", "", $user_supplied);
The input validation vulnerability inside escapeshellcmd() and
escapeshellarg() on Win32 platform has been resolved. A new PHP version
(4.3.7) immune to this vulnerability is due to be released on June 3rd,
The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0542 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
04/05/2003 Vulnerability acquired by iDEFENSE
05/07/2004 iDEFENSE clients notified
05/07/2004 Initial vendor notification
05/17/2004 Initial vendor response
05/17/2004 Public disclosure
3APA3A is credited with this discovery.
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