Modsecurity Cross Site Scripting Bypass Vulnerability

# Product: Mod_security
# Author: Rafay Baloch
# Company: RHAINFOSEC
# Website: http://services.rafayhackingarticles.net
# Reported: 8/8/2013
# Fixed: 25/8/2013
# Status: Fixed

============
Introduction
============

The Mod_Security firewall is one of the most known WAF around, It has
anonline smoke test where we can check if a vector bypassed the regular
expressions that are meant to block the attacks. Recently,
Modsecurity setup a challenge for researchers, the challenge was
divided into two parts.

1) Bypassing Modsecurity's Firewall
2) Bypassing MentalJS

Luckily, i managed to bypass both of them.

=======
Details
=======

The modsecurity's rules were very strict, therefore i had to use a browser
bug to crack modsecurity's challenge. The browser bug involved
using seprators just before an event handler. I tried with lots of
seprators, however only /x0b worked for me in this case.

===
POC
===

<a[\x0b]onmouseover=location='\x6A\x61\x76\x61\x73\x63\x72\x69\x70\x74\x3A\x61\x6C\x65\x72\x74\x28\x30\x29\x3B'>rhainfosec

===
Fix
===

The ModSecurity has updated the rule set and it now the detects the vector
as an xss vector. Along with that i also provided modsecurity with the list
of seprators that may have allowed for an attacker to create a working
bypass in other browsers too.

#  0day.today [2018-02-15]  #