Waraxe IT Security Portal  
  Login or Register
::  Home  ::  Search  ::  Your Account  ::  Forums  ::   Waraxe Advisories  ::  Tools  ::
May 22, 2024
 Members List
 IRC chat
 Base64 coder
 MD5 hash
 CRC32 checksum
 ROT13 coder
 SHA-1 hash
 Sql Char Encoder
 y3dips ITsec
 Md5 Cracker
 User Manuals
 Recommend Us
 Your Account

User Info
Welcome, Anonymous

Latest: MichaelSnaRe
New Today: 0
New Yesterday: 0
Overall: 9145

People Online:
Visitors: 385
Members: 0
Total: 385
PacketStorm News
·301 Moved Permanently

Log in Register Forum FAQ Memberlist Search
IT Security and Insecurity Portal

www.waraxe.us Forum Index -> PhpNuke -> [waraxe-2006-SA#045] - Bypassing CAPTCHA in phpNuke 6.x-7.9
Post new topic  Reply to topic View previous topic :: View next topic 
[waraxe-2006-SA#045] - Bypassing CAPTCHA in phpNuke 6.x-7.9
PostPosted: Sat Feb 18, 2006 2:25 pm Reply with quote
Site admin
Site admin
Joined: May 11, 2004
Posts: 2407
Location: Estonia, Tartu

{ [waraxe-2006-SA#045] }
{ }
{ [ Bypassing CAPTCHA in phpNuke 6.x-7.9 ] }
{ }

Author: Janek Vind "waraxe"
Date: 18. February 2006
Location: Estonia, Tartu
Web: http://www.waraxe.us/advisory-45.html

Target software description:

phpNuke 6.0 - 7.9

Homepage: http://phpnuke.org/

What is phpNuke ?

PHP-Nuke is a news automated system specially designed to be used in Intranets and
Internet. The Administrator has total control of his web site, registered users, and
he will have in the hand a powerful assembly of tools to maintain an active and 100%
interactive web site using databases.


So what's the CAPTCHA? From wikipedia: http://en.wikipedia.org/wiki/Captcha

A captcha (an acronym for "completely automated public Turing test to tell computers
and humans apart") is a type of challenge-response test used in computing to determine
whether or not the user is human. The term was coined in 2000 by Luis von Ahn, Manuel
Blum, and Nicholas J. Hopper of Carnegie Mellon University, and John Langford of IBM.
A common type of captcha requires that the user type the letters of a distorted and/or
obscured sequence of letters or digits that appears on the screen.

Phpnuke is using very simple form of CAPTCHA (called "security code"), which will try
to resist against automated actions - login bruteforce, account creation DoS, ect.
As usual, we can use OCR software for "guessing" the security code. In most of the cases
this will succeed, but what is more important - phpNuke's CAPTCHA has very big design flaw.
It appears, that nuke CAPTCHA's challenge and response are reusable as many times as we


Let's look at source ("mainfile.php" line ~ 898):

----------------[ from source code ]------------------

function loginbox() {
global $user, $sitekey, $gfx_chk;

mt_srand ((double)microtime()*1000000);
$maxran = 1000000;
$random_num = mt_rand(0, $maxran);
$datekey = date("F j");
$rcode = hexdec(md5($_SERVER['HTTP_USER_AGENT'] . $sitekey . $random_num . $datekey));
$code = substr($rcode, 2, 6);

----------------[ /from source code ]-----------------

We can see, that challenge is called "$random_num" and response "$code" is constructed
from various parts. And this algrithm means, that some specific challenge will have same
response in following conditions:

1. It must be same day (because of the "$datekey")
2. HTTP_USER_AGENT must be the same

So how to exploit this design weakness. First we need working challenge/response pair
from "victim" server. For this let's look at CAPTHA picture with numbers at login page.
Right mouse click on that picture and (in case of IE) --> properties-->address , and we
can see picture url, something like this:


Let's write down "random_num", this is our challenge number. Now just look at the same picture and
you will see response number, in this case "304380".
So challenge/response pair for this day is 112652/304380.
And then just implement this knowledge in script or whatever else. As example, there is
html code for very simple proof of concept:

[------ real life exploit ------]

<title>phpNuke CAPTHCA bypass POC</title>

<form action="http://localhost/nuke78/modules.php?name=Your_Account" method="post">

Username: <input type="text" name="username" size="15" maxlength="25"><br>
Password: <input type="password" name="user_password" size="15" maxlength="20"><br>

<input type="hidden" name="random_num" value="112652">
<input type="hidden" name="gfx_check" value="304380">

<input type="hidden" name="op" value="login">
<input type="submit" value="Login">


[----- /real life exploit ------]

See ya next time and have a nice day ;)

How to fix:

There is no easy way to write bulletproof CAPTCHA for phpnuke. Let's hope, that
8.x branch will bring some better solutions.


Greetz to LINUX, Heintz, y3dips, shai-tan, slimjim100, zer0-c00l and
all other active members from waraxe forum !

Raido Kerna - tervitused!

Additional resources:

HDD data recovery - http://www.hdd911.com/

DX expeditions database - http://www.dxdb.com/


Janek Vind "waraxe"

Homepage: http://www.waraxe.us/

---------------------------------- [ EOF ] ------------------------------------

Last edited by waraxe on Fri Apr 13, 2007 4:21 pm; edited 1 time in total
View user's profile Send private message Send e-mail Visit poster's website
PostPosted: Wed Feb 22, 2006 1:03 am Reply with quote
Joined: May 24, 2004
Posts: 404
Location: Caiman

very smart exellent job janek Cool
View user's profile Send private message Visit poster's website
PostPosted: Thu Feb 23, 2006 10:54 am Reply with quote
Valuable expert
Valuable expert
Joined: Feb 22, 2005
Posts: 477

Always been a greaser havent you LINUX? Razz


?In short: just say NO TO DRUGS, and maybe you won?t end up like the Hurd people.? -- Linus Torvalds
View user's profile Send private message
[waraxe-2006-SA#045] - Bypassing CAPTCHA in phpNuke 6.x-7.9
  www.waraxe.us Forum Index -> PhpNuke
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
All times are GMT  
Page 1 of 1  

 Post new topic  Reply to topic  

Powered by phpBB 2001-2008 phpBB Group

Space Raider game for Android, free download - Space Raider gameplay video - Zone Raider mobile games
All logos and trademarks in this site are property of their respective owner. The comments and posts are property of their posters, all the rest (c) 2004-2020 Janek Vind "waraxe"
Page Generation: 0.149 Seconds