Today I delivered the “Solid as Diamond: use ruby in a web application penetration test” talk in the Fiera della tecnologia ICT fair in Milan, Italy.

It was supposed to be an not-too-much formal, innovative (as conference template) fair in a too much business oriented scenario in ICT fairs in Milan.

The event missed some of its targets, but I will discuss in an ad hoc post in my Italian blog.

The talk I delivered was the one I gave ad Railsberry 2013 in Cracow, April 2013.

Talk outline

For both the events I used a broken web application written in Sinatra. The code is of course opensource and published on this github repository.

``` ruby the vulnerable web application code require ‘sinatra’

configure do enable :sessions end

get ‘/’ do redirect ‘/login’ end get ‘/logout’ do session[:logged] = nil redirect ‘/login’ end

get ‘/users’ do erb :users end

get ‘/users/:name’ do redirect ‘/home’ unless params[:name] == ‘tom’ or params[:name] == ‘mark’ or params[:name]==’john’ redirect “/hello?name=#{params[:name]}”


get ‘/hello’ do if ! session[:logged] @message=”You must login first” erb :login end

@name = params[:name] erb :hello end

get ‘/login’ do @message=”” erb :login end

post ‘/login’ do

ret = check_creds(params[“login”], params[“password”])

if ret == 0 session[:logged]=params[“login”] redirect ‘/home’ end

@message = “Wrong password for #{params[“login”]} user” if ret == 1 @message = “Unknown username #{params[“login”]}” if ret == -1 erb :login end

get ‘/robots.txt’ do headers “Content-Type”=>”text/plain” “User agent: *\nDisallow: /backend\nDisallow: /log\nDisallow: /db\nAllow: *\n” end

get ‘/home’ do if session[:logged].nil? @message=”You must login first” redirect ‘/login’ end erb :home end

get ‘/backend’ do

erb :backend end

get ‘/log’ do if session[:logged].nil? @message=”You must login first” redirect ‘/login’ end

erb :log end

get ‘/db’ do if session[:logged].nil? @message=”You must login first” redirect ‘/login’ end

erb :db end

def check_creds(username, password) ret = 0 users = File.readlines(‘db/creds.txt’) users.each do |u| u=u.chomp return 0 if u.split(‘:’)[0] == username and u.split(‘:’)[1] == password return 1 if u.split(‘:’)[0] == username and u.split(‘:’)[1] != password end

return -1 end

To the audience I saw that the only information they have is the url to attack ``` http://localhost:4567 ``` and eventually a valid username.

### Prerequisite

This assumption is valid for a pentest you deliver to your customer; to be more
effective you'll be given of a regular user.
In case you don't have it, you can eventually register a new one on the
website. Finally if no registration is possible you have to blind bruteforce a
valid username. Good luck.

### First goal is to leverage the attack surface and to understand the underlying technology

We saw that it's possible to fingerprint a web application technology seeing
how the answer you get back requesting a web page, let's say the website root.
To gather all the information you can, I wrote the [gengiscan gem](

Running gengiscan specifying the target here it is the result:

$ gengiscan http://localhost:4567

So our target is a ruby written web application powered by WEBrick server.

We will get further information using the robots.txt file if available. I wrote
the [codesake_links gem]( you can
use either to fetch a robots.txt looking for open urls and to bruteforce the
target with a given dictionary.

$ links -r http://localhost:4567
[] links v0.71 (C) 2013 - is starting up at 16:59:42 16:59:42 [] found 3 disallowed url(s) on http://localhost:4567 16:59:42 [] /backend - 200 16:59:42 [] /log - 302 16:59:42 [] /db - 302 [] leaving at 16:59:42

Using the robots.txt, it seems developers forget to place proper redirection on
the ``` /backend ``` url. This can be interesting in a second scanning step to
try to guess backend users weak passwords.

We will also use a url dictionary to find some other urls to use.

$ links -b support/test_case_dir_wordlist.txt http://localhost:4567 [] links v0.71 (C) 2013 - is starting up at 17:02:36 17:02:36 [] http://localhost:4567/users: Open (7 msec)

As first step, we had that 

* technology used is ruby and we have also the application server vendor
* we found /backend and /users links with just a couple of HTTP requests.

### Second goal is to find some regular users using user enumeration attack

Our web application [is vulnerable to user enumeration]( since
it gaves two different error messages if the username is valid but the password
is not and in case both data are wrong.

I wrote a quick script available on the broken web application repository,
called ``` http_login_bruteforcer.rb ```. Check it out for futher details.
I used a regular username, tom as a canary and a dictionary of usernames you
can find everywhere in Internet.

$ ./http_login_bruteforcer.rb -P tom [] http_login_bruteforcer.rb v1.2.0 (C) 2013 - is starting up at 17:07:24 17:07:24: PID - 97376 17:07:24: existing user tom used as canary 17:07:24: 500 words from dictionary loaded 17:07:24: awake… probing with: tom 17:07:24: awake… probing with: mark 17:07:24: awake… probing with: john 17:07:24: awake… probing with: terence 17:07:24: awake… probing with: root 17:07:24: awake… probing with: administrator … 17:07:33: awake… probing with: liz 17:07:33: 5 user(s) found 17:07:33 [] tom 17:07:33 [] mark 17:07:33 [] admin 17:07:33 [] jason 17:07:33 [] mary [*] shutting down at 17:07:33

Bingo. 5 usernames found.

### Third goal is to exploit reflected cross site scripting in login and in hello pages

In hello page we noticed the name parameter you have in querystring is
reflected on resulting HTML. The same happens in the /login page with POST

We will use [cross gem]( to test for
reflected XSS.

$ cross -u http://localhost:4567/hello\?name=paolo
cross 0.35.0 (C) 2011, 2012 - Canary found in output page. Suspected XSS

$ cross http://localhost:4567/login
cross 0.35.0 (C) 2011, 2012 - Canary found in output page. Suspected XSS ```

In both cases appending a -D flag you will cause cross to dump the resulting HTML in order to double check che canary presence.

The slides

Slides are on speakerdeck website

Image courtesy by ikewinski