CVE-2016-2784

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Web Server Cache Poisoning in CMS Made Simple
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CVE-2016-2784

Product Description
===================

CMS Made Simple is a great tool with many plugins to publish content on the Web. It aims to 
be simple to use by end users and to provide a secure and robust website.

Website: http://www.cmsmadesimple.org/

Description
===========

A remote unauthenticated attacker can insert malicious content in a CMS Made Simple 
installation by poisoning the web server cache when Smarty Cache is activated by modifying 
the Host HTTP Header in his request.

The vulnerability can be triggered only if the Host header is not part of the web server 
routing process (e.g. if several domains are served by the same web server).

This can lead to phishing attacks because of the modification of the site's links, 
defacement or Cross-Site-Scripting attacks by a lack of filtering of HTML entities in 
$_SERVER variable.

**Access Vector**: remote
**Security Risk**: medium
**Vulnerability**: CWE-20
**CVSS Base score**: 5.3 (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N)

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Proof of Concept
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Request that shows improper HTML entities filtering and will insert 
' onload='javacript:alert(Xss) in the pages :

  GET / HTTP/1.1
  Host: ' onload='javascrscript:ipt:alert(Xss)
  Accept: */*
  Accept-Encoding: gzip, deflate
  Connection: close
  
Request that changes the root domain for all links and allows to redirect to external 
websites : 

  GET / HTTP/1.1
  Host: www.malicious.com
  Accept: */*
  Accept-Encoding: gzip, deflate
  Connection: close
  
Solution
========

Use the variable $_SERVER['SERVER_NAME'] instead of the variable $_SERVER['HTTP_HOST'] 
given that the server name is correctly defined or use an application specific 
constant.

Fixes
=====

Upgrade to CMS Made Simple 2.1.3 or 1.12.2.

See http://www.cmsmadesimple.org/2016/03/Announcing-CMSMS-1-12-2-kolonia and 
http://www.cmsmadesimple.org/2016/04/Announcing-CMSMS-2-1-3-Black-Point for upgrade 
instructions.

Mitigation : disable Smarty caching in the admin panel.

Affected Versions
=================

CMS Made Simple < 2.1.3 and < 1.12.2

Vulnerability Disclosure Timeline
=================================

02-24-2016: Vendor contacted
02-24-2016: Vulnerability confirmed by the vendor
03-01-2016: CVE identifier assigned
03-28-2016 & 04-16-2016: Vendor patch release
05-03-2016: Public Disclosure

Credits
=======

 * Mickaël Walter, I-Tracing (lab -at- i-tracing -dot- com)
 
 Website: http://www.i-tracing.com/