Author Archives: Soroush Dalili

About Soroush Dalili

Web application security researcher and penetration tester.

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 ysoserial.net 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: https://www.nccgroup.trust/globalassets/our-research/uk/images/whitepaper-new.pdf

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!

Story of my two (but actually three) RCEs in SharePoint in 2018

I became interested in looking at .NET deserialization issues in Jan. 2018 when a work colleague (Daniele Costa) asked me whether I had worked with the ysoserial.net tool before (and the answer was a no!). I began to like it more and more just by looking at the generated payloads, and then by reading its useful references. It even answered one of the questions that I always had in mind: “How can ViewState or EventValidation without MAC enabled lead to remote code execution?“; the answer was simple: “deserialization attacks using ObjectStateFormatter or LosFormatter”. I know I was late to the party but as the attack surface is huge, I managed to exploit a number applications including SharePoint without really having deep knowledge in this area. 

As mentioned in the MS 2018 Q4 – Top 5 Bounty Hunter for 2 RCEs in SharePoint Online post, I managed to exploit two RCEs in SharePoint Workflows that also affected SharePoint on-prem versions. Therefore, in addition to having a good bounty for the online version, I managed to get two CVEs in .NET Framework (CVE-2018-8284 and CVE-2018-8421).

Details of these vulnerabilities were published in NCC Group’s website as can be seen here:

  1. Bypassing Workflows Protection Mechanisms – Remote Code Execution on SharePoint
  2. Bypassing Microsoft XOML Workflows Protection Mechanisms using Deserialisation of Untrusted Data

The first one was a logical issue in the Workflows. This was the one with the epic Microsoft’s response:

The second one however was a deserialisation issue that was not fully exploited on SharePoint until after the advisory was published. Here is the short story:

Which was shortly followed by a fully working exploit thanks to Alvaro’s tip:

It should be noted that Microsoft had already given me the maximum bounty that is for an RCE issue even for the second one.

Finally, 2018 was a good year for me on SharePoint finding 3 RCEs in it. If you are wondering what the third one was, the clue is in the ASP.NET resource files (.RESX) and deserialization issues post. I did not receive any bounty for it despite having a reverse shell on the Microsoft SharePoint Online server due to an ongoing engagement my company (NCC Group) had with them at the same time (unlucky me but I was lucky enough to be compensated by my company as they recognised my efforts).

ASP.NET resource files (.RESX) and deserialization issues

I have recently published a blog post via NCC Group’s website about the deserialization issue by abusing the ASP.NET resource files (.resx and .resources extensions). A number of products were exploited and some file uploaders can also be vulnerable to this type of attack.

The full article can be viewed in NCC Group’s website: https://www.nccgroup.trust/uk/about-us/newsroom-and-events/blogs/2018/august/aspnet-resource-files-resx-and-deserialisation-issues/

PDF version of the blog post published by NCC Group can be downloaded from:

https://soroush.secproject.com/downloadable/aspnet_resource_files_resx_deserialization_issues.pdf

In addition to this, the advisories can be seen via:

Code Execution by Unsafe Resource Handling in Multiple Microsoft Products: https://www.nccgroup.trust/uk/our-research/technical-advisory-code-execution-by-unsafe-resource-handling-in-multiple-microsoft-products/

Code Execution by Viewing Resource Files in .NET Reflector: https://www.nccgroup.trust/uk/our-research/technical-advisory-code-execution-by-viewing-resource-files-in-net-reflector/

I had also reported the same vulnerability in Telerik justDecompile and JetBrains dotPeek:

https://blog.jetbrains.com/dotnet/2018/08/02/resharper-ultimate-2018-1-4-rider-2018-1-4-released/

https://www.telerik.com/support/whats-new/justdecompile/release-history/justdecompile-r2-2018-sp1

Relevant tweets about this:

MS 2018 Q4 – Top 5 Bounty Hunter for 2 RCEs in SharePoint Online

I was amongst top 5 bounty hunters in MS Q4 2018: https://blogs.technet.microsoft.com/msrc/2018/07/26/recognizing-q4-top-5-bounty-hunters/

Although I am not doing active bug bounty hunting at the moment, this was a great experience. I got this prize because of reporting two RCEs in SharePoint Online.

One of the RCEs was patched in MS July 2018 patch (CVE-2018-8284) and this was an interesting screenshot:

I did not get any prize for CVE-2018-8300 which was another RCE in SharePoint using the resource files (the issue was similar to a bug reported in another MS project that I was part of its paid engagement).