SPIP 3.1.2 Cross Site Scripting

`## 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 <[email protected]>  
  
GPG :  
47D1 E124 C43E F992 2A2E  
1551 8EB4 8CD9 D5B2 59A1  
  
* Website: https://sysdream.com/  
* Twitter: @sysdream  
  
  
  
`