Don’t Click That Link!

Posted by Brett Hardin on 30th June 2009

Reading time: 3 – 4 minutes

Photo: B.G. Lewandowski

Photo: B.G. Lewandowski

Why did you just click that link? Most likely you have came to this site by clicking a link from another site. Why did you do that? Did you trust the person who sent you the link? Did you click a link from Twitter, Facebook, or an email someone sent you?

When you click a link, you are telling your browser, “I trust this person.” However, this is not the way we use the Internet. We click on links all the time. We click on links from “untrusted” sources. We click links from people we don’t know and we even click on URL’s that have been modified. On Twitter, a person is much more inclined to click the shortened link http://bit.ly/5hXRW then they are to click http://somewherebank.com/transfer.jsp?amount=1000&to_account=56777564. Even though the shortened link could redirect to the somwherebank.com site.

But, why would someone trick you into clicking a cleverly disguised link? The site that you are redirected to may seem harmless. It could also be extremely malicious.

What happens if this page, (the one you are currently viewing), was filled with Cross-Site Request Forgery (CSRF) links? This web page could be setup with all types of malicious intent. However, you didn’t know that when clicking the link. Now, it is too late.

If this site did have Cross-Site Requests, I could do things such as:

  • Change the password on your Facebook account
  • Transfer the money from your on-line bank account to another account
  • Enact trades from a financial institution such as E*Trade

The sites that I exploit would have to be vulnerable to CSRF. But researchers, such as Mike Bailey and Russ McRee, are constantly finding CSRF vulnerabilities in web applications.

An example of how clicking links from untrusted sources is never good was demonstrated in Billy Rios and Nitesh Dhanjani, Bad Sushi talk. In their presentation they described sending phishers a word document stating their account numbers were inside. They sent this email to 25 known phishers. 10 of the phishers opened the word document and were presented with this. In addition, there was another link that said, “Actually, my account information is here.” 3 of the 10 clicked on that link. Even the phishers click links they shouldn’t.

What should be done? Who knows. It is human nature to trust people and we can’t get things done if every time someone sends us a link we open up a VMware image to view a link. So continue using the Internet the way you have been and remember, “These aren’t the droids your looking for.”

Categories: General Thoughts, Primer, Social Networks, Web Application Security
Tags: , , , , , ,
30Jun

Buzzword: FUD – Fear, Uncertainty, and Doubt

Posted by Brett Hardin on 23rd June 2009

Reading time: 1 – 2 minutes

Photo: crowolf

Photo: crowolf

FUD is becoming a very common acronym to hear in security circles. The acronym FUD has been popping up on Blog postings, emails, tweets, and at security conferences.

FUD is an acronym that stands for Fear, Uncertainty, and Doubt. The phrase describes marketing schemes that are focused on using Fear, Uncertainty, and Doubt to sell a product. Good example of FUD are sensational headlines such as, “Conficker Now Instructed to Steal” or more famously, “Hackers Can Turn your Home Computer into a Bomb!”

With FUD campaigns the marketer is attempting to use FUD to sell something. This marketed item could be a “security” product or FUD can be used to create a buzz around the “item at hand.”

One quick way to identify FUD is spotting a headline or article that is greatly sensationalized, has a lot of speculation, or makes gross generalizations. The other critical factor in FUD is there is a lack of information in the article. FUD articles clearly point out the problem, but fail to point out how the author arrived at this conclusion.

Fear, Uncertainty, and Doubt pray on human emotions and marketing campaigns that exploit this will not be going away any time soon.

Categories: Buzzwords, Primer
Tags: , , , ,
23Jun

XSS – Understanding Cross Site Scripting

Posted by Brett Hardin on 21st May 2009

Reading time: 4 – 6 minutes

XSS Understanding Cross Site ScriptingXSS Understanding Cross Site ScriptingXSS Understanding Cross Site Scripting

If it hasn’t already, Cross-Site Scripting (XSS) will soon be replacing SQL injection as the new buzzword in the security sector. XSS will continually be a topic on this blog as well as others [1],[2],[3],[4]. Due to this fact, I think a primer would be a good idea for those who don’t know or understand this problem.

Many articles have been written about Cross-Site Scripting and if you want to have a better understanding of the problem, I suggest you read those documents (Links at the bottom of the post).

Basically, There are 3 types of Cross-Site Scripting:

  1. Stored/Non-Reflective/Persistent Cross Site Scripting (User visits the XSS’ed page)
  2. Non-Stored/Reflective/Reflected Cross Sited Scripting (User clicks a link that embeds the script into the loaded page)
  3. DOM Based Cross Site Scripting (please read this article)

All of these names make it confusing for a first timer to understand XSS. There really should be a better web application security standards organization. Here is a breakdown of Persistent XSS and Reflective XSS. These are the big two that most people talk about when they are referring to Cross Site Scripting. If you understand these well, you will be able to participate in 90% of XSS conversations.

Persistent Cross-Site Scripting
Persistent XSS is arguably more dangerous than reflective XSS. This attack embeds the malicious script permanently into the web application. The script will then wait until people access the page it is located on.

Here is an attack using Persistent Cross-Site Scripting:

  1. The victim visits a website they trust, amazon.com.
  2. A script has been inserted by an attacker on a page they happen to visit while on amazon.com.
  3. The script executes in the context of amazon.com.
  4. The victim is then compromised.

Note: Obviously, someone can increase the chances of the victim visiting this page (step 2) through social engineering, phishing, etc.

Reflective Cross-Site Scripting
These are the ones the media usually reports on. [1],[2],[3]. In this attack, some type of social engineering is involved for the attack to be successful.

Here is an attack, using Reflective Cross-Site Scripting:

  1. The victim gets an email/Instant Message that contains a link.
  2. The victim clicks the link. (Requires User Intervention)
  3. A script has been inserted by an attacker on the page they then visit.
  4. The script executes in the context of that site.
  5. The victim is then compromised.

Note: I want to reiterate that this attack requires some type of user intervention (step 2).

Why is Cross-Site Scripting Bad?
Cross-Site Scripting can lead to all sorts of different exploits, including system compromise. For an attacker to do this, they need to break out of the browser’s context. We have seen examples that breaking out of the browser is not that hard to do.

In addition, an attacker can also establish a bi-directional channel using iframes. This creates a man-in-the-middle attack. The attacker can then intercept key strokes, use the victim as an intranet portscanner, and even stealing creditials. The attacker is only limited by their knowledge of scripting.


XSS Understanding Cross Site Scripting

Example of a bi-directional channel

Hopefully, this gives you a better understanding of Cross-Site Scripting. Feel free to leave comments if you don’t understand something and I will address it in the article.

Additional Resources:
Cross-Site Scripting (XSS) FAQ
OWASP Guide to XSS
XSS tutorial
XSS Video Tutorial (via youtube)
XSS Attack API

Categories: Buzzwords, OWASP, Primer, Vulnerabilities, Web Application Security
Tags: , , , , , , , , , , , , ,
21May
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