## SPIP 3.1.2 Reflected Cross-Site Scripting (CVE-2016-7981)

### 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 `var_url` parameter of the `valider_xml` file is not correctly sanitized and can be used to trigger a reflected XSS vulnerability.

**Access Vector**: remote

**Security Risk**: medium

**Vulnerability**: CWE-79

**CVSS Base Score**: 6.8 (Medium)

**CVE-ID**: CVE-2016-7981

### Proof of Concept

    http://spip-dev.srv/ecrire/?exec=valider_xml&var_url=%22%3E%3Ch1%3EXSS!%3C/h1%3E

### Vulnerable code

The `$url variable` is not properly sanitized in `valider_xml.php`, line 134 :

    $res =
      "<div style='text-align: center'>" . $err . "</div>" .
      "<div style='margin: 10px; text-align: left'>" . $texte . '</div>';
    $bandeau = "<a href='$url_aff'>$url</a>";

The Cross-Site Scripting vulnerability is triggered on line 146 :

    echo "<h1>", $titre, '<br>', $bandeau, '</h1>',


### 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 : Incorrect fix from SPIP Team.
* 27/09/2016 : New proof of concept for bypassing fixes for XSS sent.
* 27/09/2016 : Fixes issued for XSS (23185).
* 30/09/2016 : SPIP 3.1.3 Released

### Fixes

* https://core.spip.net/projects/spip/repository/revisions/23200
* https://core.spip.net/projects/spip/repository/revisions/23201
* https://core.spip.net/projects/spip/repository/revisions/23202


### 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