NGS00500 Technical Advisory: Bit51 Better WP Security Plugin - Unauthenticated Stored XSS to RCE

[NCC Group Research <research@xxxxxxxxxxxx>]

=======
Summary
=======
Name: Bit51 Better WP Security Plugin - Unauthenticated Stored XSS to RCE
Release Date: 30 July 2013
Reference: NGS00500
Discoverer: Richard Warren <richard.warren@xxxxxxxxxxxx>
Vendor: Bit51
Vendor Reference: 
Systems Affected: Bit51 Better WP Security Plugin Version 
3.4.8/3.4.9/3.4.10/3.5.2/3.5.3
Risk: High
Status: Published

========
TimeLine
========
Discovered:  1 April 2013
Released:  1 April 2013
Approved:  1 April 2013
Reported:  1 April 2013
Fixed: 21 July 2013
Published: 30 July 2013

===========
Description
===========
Bit51 Better WP Security Plugin Version 3.4.8/3.4.9/3.4.10/3.5.2/3.5.3  -
Unauthenticated Stored XSS to RCE

I. VULNERABILITY
-------------------------
The Better Security Wordpress Plugin suffers from a stored XSS
vulnerability, which can be exploited by a remote unauthenticated attacker
to steal cookies or gain privileged access to the affected site.

II. BACKGROUND
-------------------------
Better WP Security takes the best WordPress security features and
techniques and combines them in a single plugin thereby ensuring that as
many security holes as possible are patched without having to worry about
conflicting features or the possibility of missing anything on your site.

With one-click activation for most features as well as advanced features
for experienced users Better WP Security can help protect any site.

http://bit51.com/software/better-wp-security/

=================
Technical Details
=================
The Better Security Wordpress plugin logs all 404 errors within the "logs"
tab. By purposefully requesting a non-existent page containing an XSS
payload a 404 error will be generated. When the admin clicks on the logs
lab, the XSS payload will be triggered and cookies can be stolen, or some
onsite request forgery can be carried out to gain admin access. Note -
there are possibly a few other vectors for XSS through the logs. In
addition to 404s, username login attempts, user-agents and other
potentially interesting parameters are logged.

Single quotes are escaped, but this can be bypassed easily. Also the
request must be made through burp or a script as browsers will URL encode
it. A proof of concept request can be found below:

==============================================================

GET
/xss.php?payload="><script>alert(String.fromCharCode(88,83,83))</script>
HTTP/1.1
Host: example.com
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:15.0)
Gecko/20100101 Firefox/15.0.1
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Proxy-Connection: keep-alive
Cookie: wordpress_cookies.....

===============================================================

===============
Fix Information
===============
Better WP Security 3.5.4 has been released, which includes a fix for this issue.


NCC Group Research
http://www.nccgroup.com/research


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