Yet Other Examples of Abusing CSRF in Logout

The “Login/logout CSRF: Time to reconsider?” blog post by Mathias Karlsson (@avlidienbrunn) is a great resource that shows why sometimes CSRF in logout/login can be considered as an impactful security issue and how it can be abused.

In Mathias’ blog post, unauthenticated XSS can also be exploited similar to the self-XSS issue but it is less complicated. This is when a  XSS is not accessible to authenticated users. In that case, the attacker logs the user out to deliver the XSS payload which waits for the user to authenticate in another tab in order to perform the ultimate attack.

Recently, I found another similar but rare example to perform CSRF attacks in a “secure” website that required logging victims out and waiting for them to log back in later. Although this case is not as common as the examples described by Matthias, it is still a valid case to consider during an assessment.

The websites I was testing had an anti-CSRF token in every POST requests that changed per-session, per-request, and per-page. However, as the logout page used a GET request it was vulnerable to CSRF attacks. The web application kept the anti-CSRF token value in the user’s session on the server-side, and GET and POST requests were not interchangeable.

All was good until I realised that some of the previously captured POST requests can be replayed with a new authenticated session cookie if I remove the anti-CSRF token’s parameter from the body of the POST request. I could however only send one token-less POST request to each page as I received a security error afterwards. This showed that the website was creating an anti-CSRF token for a page upon accessing the page for the first time (there was also a page that could generate an anti-CSRF token for a given page using AJAX but that is not important here).

As a result, I could not exploit this issue if the victim had already browsed a page that I wanted to target. However, as the logout page was vulnerable to CSRF attacks, I could exploit this issue by tricking the victim to visit a malicious website that would:

  • Send a malicious POST request to the website without an anti-CSRF token’s parameter just in case I was very lucky and the victim had not browsed that particular page (very unlikely as it had a few pages)
  • Log the victim out of the target website
  • Keep sending the malicious POST request without the anti-CSRF token’s parameter to perform an action in the background until the user logs back in the target website in another browser tab

How to win BIG and even more!

I recently had a presentation in the OWASP Birmingham (UK) chapter meeting. The crowd was very friendly, and it was a good experience overall with a lot of free food! I definitely recommend attending the next one if you are close by.

In my presentation, I showed a few examples how I managed to win a lot of money in gambling games, cheated when doing my online shopping, and got more free gifts than necessary! Obviously all of my actions were as part of defined security assessments, and therefore I legally had the necessary permissions to carry out my tests.

My presentation’s description was:

I am going to review a number of interesting flaws that I have seen within the payment systems and gambling games. This includes examples that allowed me to win big while I was gambling very responsibly as well as simple methods that brought me free goods such as expensive books that I really didn’t need, fake moustaches, or even caskets for my fake funeral!

Disclaimer: all issues were reported responsibly to the companies and no moustache or slot machine was harmed in this process! I am not going to name any companies during this presentation.

Its slides are available via the SlideShare website:

After this presentation, Ashley Cox and I performed a research for NCC Group about abusing voucher codes. As a result, we also made the following blog post: Online shoplifting – exploiting e-commerce basket and voucher faults for five-finger discount.

Perhaps this how some people find glitches to post in the hotukdeals website!

I have also updated the whitepaper I had created for testing financially-oriented web applications to cover more discovered test-cases. This freely accessible guideline has been created for penetration testers and bug bounty hunters to assess ecommerce and financial services applications:

I would personally be grateful if you could give a reference to me or this whitepaper if you have found it useful or you have managed to identify a vulnerability using this.

Finding and Exploiting .NET Remoting over HTTP using Deserialisation

I have published a blog post in NCC Group’s website to explain how to test deserialisation issues within the SOAP requests that are used by ASP.NET Remoting over a HTTP channel:

This research is accompanied by an open source project that show a sample vulnerable server and a client that can be useful for testing purposes:

The blog link is as follows:

More research on .NET deserialization

I have recently published a whitepaper and a blog post as part of work research in NCC Group’s website. A number of plugins have also been added to the project.

The whitepaper can aid security researchers as well as developers to find more deserialisation issues in .NET applications by identifying built-in methods or classes that can be abused in this process. The whitepaper can be downloaded from:

In the blog post, I have also explained one of the most interesting findings of the research with which code could be executed upon pasting an object from the clipboard:

Feel honoured to be there again after 8 years: Top 10 Web Hacking Techniques of 2017

I thought I should document this whilst we are still in 2018…

We used to have Top 10 Web Hacking Techniques every year but it suddenly stopped! After having a private conversation with James Kettle in Twitter, he decided to stand up for this and PortSwigger (the company behind Burp Suite) kindly supported it. The full story can be read here: Top 10 Web Hacking Techniques of 2017 – Nominations Open

I was lucky enough to be on the voting panel despite having a nomination (I couldn’t vote for myself obviously). In the end, I felt honoured that my request encoding technique to bypass WAFs came in the Top 10 2017 (#8 to be exact). There were seriously good research works and I recommend you to check them out: Top 10 Web Hacking Techniques of 2017

I have always tried to share with the AppSec community as that also enable me to learn more by reading other people’s work or research. The last time I was on the Top 10 was 2009 for the IIS semicolon bug (remember file.asp;.txt bypass technique on IIS6?) so good to be back (#6): Top Ten Web Hacking Techniques of 2009 (Official) 

Although there has always been discussions on the type of submissions such as techniques vs one time vulnerabilities as well as voting patterns, having a list of web related submissions is always useful and we now have it for 2017!