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Hi,

We have recently discovered a Remote Code Execution vulnerability
in Moodle 1.9.3.

We follow a responsible disclosure policy that consists in notifying the
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Make us aware when the fix is ready and tested!

We try to synchronize the disclosure time with the vendor, if the
details of the vulnerability becomes public we will immediately disclose
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Detailed informations follow (advisory draft, do not publish).

Regards,
Antonio 's4tan' Parata
http://www.ush.it

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Moodle 1.9.3 Remote Code Execution
 
Name Remote Code Execution in Moodle
Systems Affected Moodle 1.9.3 and possibly earlier versions
Severity High
Impact (CVSSv2) High 7.3/10, vector: (AV:N/AC:L/Au:M/C:P/I:P/A:C)
Vendor http://moodle.org/
Advisory http://www.ush.it/team/ush/hack-moodle193/moodle193.txt
Authors Antonio "s4tan" Parata (s4tan AT ush DOT it)
                  Francesco "ascii" Ongaro (ascii AT ush DOT it)
                  Giovanni "evilaliv3" Pellerano (evilaliv3 AT
                  digitalbullets DOT org)
Date YYYYMMDD

I. BACKGROUND

>From the Moodle web site: "Moodle is a course management system (CMS) -
a free, Open Source software package designed using sound pedagogical
principles, to help educators create effective online learning
communities".

II. DESCRIPTION

A Remote Code Execution exists in Moodle 1.9.3.

III. ANALYSIS

- Remote Code Execution (RCE) in texed.php (pathname parameter)

A Remote Code Execution (RCE) vulnerability has been found in
filter/tex/texed.php. In order to exploit this vulnerability
register_globals must be enabled as the "TeX Notation" filter.

All these conditions reduce the impact of the vulnerability, to remark
this fact we have set "multiple authentication" flag in the cvss2 score).

In texed.php we find the following instructions:

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

$cmd = tex_filter_get_cmd($pathname, $texexp);
system($cmd, $status);

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

Where the function "tex_filter_get_cmd", defined in lib.php, is the
following:

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

function tex_filter_get_cmd($pathname, $texexp) {
    $texexp = escapeshellarg($texexp);
    $executable = tex_filter_get_executable(false);

    if ((PHP_OS == "WINNT") || (PHP_OS == "WIN32") || (PHP_OS ==
"Windows")) {
        $executable = str_replace(' ', '^ ', $executable);
        return "$executable ++ -e \"$pathname\" -- $texexp";

    } else {
        return "\"$executable\" -e \"$pathname\" -- $texexp";
    }
}

--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--8<--

As we can see no check is performed on the "$pathname" parameter neither
in "texed.php" neither in the "tex_filter_get_cmd" function declared in
"lib.php".

Seen this it's possible to exploit this vulnerability to execute
arbitrary commands on the target server. The following urls are proof
of concept for Linux and Windows:

On Linux:
http://127.0.0.1/moodle/filter/tex/texed.php?formdata=foo&pathname=foo";ls+-l;echo+"

On Windows:
http://www.example.com/moodle/filter/tex/texed.php?formdata=foo&pathname=foo"+||+dir+||+echo+

This RCE is "blind". You'll never see the list dir of the example
because there is no print of the system command output.

IV. DETECTION

Moodle 1.9.3 and possibly earlier versions are vulnerable.

V. WORKAROUND

Proper input validation will fix the vulnerabilities.

Upgrade to latest development version.

VI. VENDOR RESPONSE

--

VII. CVE INFORMATION

No CVE at this time.

VIII. DISCLOSURE TIMELINE

20080121 Bug discovered

IX. CREDIT

Antonio "s4tan" Parata, Francesco "ascii" Ongaro and Giovanni
"evilaliv3" Pellerano are credited with the discovery of this
vulnerability.

Antonio "s4tan" Parata
web site: http://www.ictsc.it/
mail: s4tan AT ictsc DOT it, s4tan AT ush DOT it

Francesco "ascii" Ongaro
web site: http://www.ush.it/
mail: ascii AT ush DOT it

Giovanni "evilaliv3" Pellerano
mail: evilaliv3 AT digitalbullets DOT it

X. LEGAL NOTICES

Copyright (c) 2008 Francesco "ascii" Ongaro

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without mine express
written consent. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically,
please email me for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.