Crack .NET assemblies on the fly

Hi, I recently have been into a DEFCON 1 situation and I want to share with you my experience.

Basically imagine a production .net assembly that does the job quietly for 5-6 years and one day it decides to stop working ,this means that an entire segment of the business of a large enterprise is completely blocked…

To this add that developer of that assembly no longer works in the company, nobody knows where the source code can be and actually there is no  documentation.

So they call me and I felt like this:

So downloaded ILSpy and I started looking into the code while gathering the logs and checking the exceptions.

Thanks to some very lucky combo of checks I was able to figure out where the problem was in a couple of hours (windows update I hate you), but in the mean time the pressure bar was rising and the client was just going crazy. So I remembered that one time I used a tool called reflexil to fix on the fly an assembly, but later I figured out that it works nice with reflector but not with IlSpy…

However thanks to this post I was able to download a version of reflexil that was compatible with IlSpy and problem solved!

Here is a screenshot of the two working together :

ILSpyReflexil

It’s actually a great combo and I can’t wait to have the final bits.

PS : The code that you see it’s not the client’s code of course 🙂

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