1. How To Decompile An Exe

A friend of mine downloaded some malware from Facebook, and I'm curious to see what it does without infecting myself. I know that you can't really decompile an .exe, but can I at least view it in Assembly or attach a debugger?

Dec 03, 2018  Decompiler for Autoit.exe Sign in to follow this. Decompiler for Autoit.exe. By 24terminator96. 24terminator96, the point being made is that discussion of decompiling AutoIt scripts violates the rules of this forum. You will not receive any assistance on this subject. √-1 2^3 ∑ π, and it was delicious! Sep 30, 2015  Follow ExeToC Decompiler. ExeToC Decompiler Web Site. Other Useful Business Software. Flex Delivers What You Need. The first fully-programmable contact center platform. A cloud-based contact center platform that’s infinitely flexible and instantly deployable Flex delivers what you need to run an omnichannel contact center out-of. AutoHotKey was developed from AutoIT and so scripts are nearly the same. Drag the compiled *.exe or *.a3x into the AutoIT Script Decompiler textbox.

Edit to say it is not a .NET executable, no CLI header.

15 Answers

With a debugger you can step through the program assembly interactively.
With a disassembler, you can view the program assembly in more detail.
With a decompiler, you can turn a program back into partial source code, assuming you know what it was written in (which you can find out with free tools such as PEiD - if the program is packed, you'll have to unpack it first OR Detect-it-Easy if you can't find PEiD anywhere. DIE has a strong developer community on github currently).

Debuggers:

• OllyDbg, free, a fine 32-bit debugger, for which you can find numerous user-made plugins and scripts to make it all the more useful.
• WinDbg, free, a quite capable debugger by Microsoft. WinDbg is especially useful for looking at the Windows internals, since it knows more about the data structures than other debuggers.
• SoftICE, SICE to friends. Commercial and development stopped in 2006. SoftICE is kind of a hardcore tool that runs beneath the operating system (and halts the whole system when invoked). SoftICE is still used by many professionals, although might be hard to obtain and might not work on some hardware (or software - namely, it will not work on Vista or NVIDIA gfx cards).

Disassemblers:

• IDA Pro(commercial) - top of the line disassembler/debugger. Used by most professionals, like malware analysts etc. Costs quite a few bucks though (there exists free version, but it is quite quite limited)
• W32Dasm(free) - a bit dated but gets the job done. I believe W32Dasm is abandonware these days, and there are numerous user-created hacks to add some very useful functionality. You'll have to look around to find the best version.

Decompilers:

• Visual Basic: VB Decompiler, commercial, produces somewhat identifiable bytecode.
• Delphi: DeDe, free, produces good quality source code.
• C: HexRays, commercial, a plugin for IDA Pro by the same company. Produces great results but costs a big buck, and won't be sold to just anyone (or so I hear).
• .NET(C#): dotPeek, free, decompiles .NET 1.0-4.5 assemblies to C#. Support for .dll, .exe, .zip, .vsix, .nupkg, and .winmd files.

Some related tools that might come handy in whatever it is you're doing are resource editors such as ResourceHacker (free) and a good hex editor such as Hex Workshop (commercial).

Additionally, if you are doing malware analysis (or use SICE), I wholeheartedly suggest running everything inside a virtual machine, namely VMware Workstation. In the case of SICE, it will protect your actual system from BSODs, and in the case of malware, it will protect your actual system from the target program. You can read about malware analysis with VMware here.

Personally, I roll with Olly, WinDbg & W32Dasm, and some smaller utility tools.

Also, remember that disassembling or even debugging other people's software is usually against the EULA in the very least :)

psoul's excellent post answers to your question so I won't replicate his good work, but I feel it'd help to explain why this is at once a perfectly valid but also terribly silly question. After all, this is a place to learn, right?

Modern computer programs are produced through a series of conversions, starting with the input of a human-readable body of text instructions (called 'source code') and ending with a computer-readable body of instructions (called alternatively 'binary' or 'machine code').

The way that a computer runs a set of machine code instructions is ultimately very simple. Each action a processor can take (e.g., read from memory, add two values) is represented by a numeric code. If I told you that the number 1 meant scream and the number 2 meant giggle, and then held up cards with either 1 or 2 on them expecting you to scream or giggle accordingly, I would be using what is essentially the same system a computer uses to operate.

A binary file is just a set of those codes (usually call 'op codes') and the information ('arguments') that the op codes act on.

Now, assembly language is a computer language where each command word in the language represents exactly one op-code on the processor. There is a direct 1:1 translation between an assembly language command and a processor op-code. This is why coding assembly for an x386 processor is different than coding assembly for an ARM processor.

Disassembly is simply this: a program reads through the binary (the machine code), replacing the op-codes with their equivalent assembly language commands, and outputs the result as a text file. It's important to understand this; if your computer can read the binary, then you can read the binary too, either manually with an op-code table in your hand (ick) or through a disassembler.

Disassemblers have some new tricks and all, but it's important to understand that a disassembler is ultimately a search and replace mechanism. Which is why any EULA which forbids it is ultimately blowing hot air. You can't at once permit the computer reading the program data and also forbid the computer reading the program data.

(Don't get me wrong, there have been attempts to do so. They work as well as DRM on song files.)

However, there are caveats to the disassembly approach. Variable names are non-existent; such a thing doesn't exist to your CPU. Library calls are confusing as hell and often require disassembling further binaries. And assembly is hard as hell to read in the best of conditions.

Most professional programmers can't sit and read assembly language without getting a headache. For an amateur it's just not going to happen.

Anyway, this is a somewhat glossed-over explanation, but I hope it helps. Everyone can feel free to correct any misstatements on my part; it's been a while. ;)

Good news. IDA Pro is actually free for its older versions now:http://www.hex-rays.com/idapro/idadownfreeware.htm

Any decent debugger can do this. Try OllyDbg. (edit: which has a great disassembler that even decodes the parameters to WinAPI calls!)

x64dbg is a good and open source debugger that is actively maintained.

Sure, have a look at IDA Pro. They offer an eval version so you can try it out.

If you are just trying to figure out what a malware does, it might be much easier to run it under something like the free tool Process Monitor which will report whenever it tries to access the filesystem, registry, ports, etc...

How To Decompile An Exe

Also, using a virtual machine like the free VMWare server is very helpful for this kind of work. You can make a 'clean' image, and then just go back to that every time you run the malware.

What you want is a type of software called a 'Disassembler'.

Quick google yields this: http://www.geocities.com/~sangcho/disasm.html

You may get some information viewing it in assembly, but I think the easiest thing to do is fire up a virtual machine and see what it does. Make sure you have no open shares or anything like that that it can jump through though ;)

I can't believe nobody said nothing about Immunity Debugger, yet.

Immunity Debugger is a powerful tool to write exploits, analyze malware, and reverse engineer binary files. It was initially based on Ollydbg 1.0 source code, but with names resoution bug fixed. It has a well supported Python API for easy extensibility, so you can write your python scripts to help you out on the analysis.

Also, there's a good one Peter from Corelan team wrote called mona.py, excelent tool btw.

If you want to run the program to see what it does without infecting your computer, use with a virtual machine like VMWare or Microsoft VPC, or a program that can sandbox the program like SandboxIE

If you have no time, submit the malware to cwsandbox:

HTH

You can use dotPeek, very good for decompile exe file. It is free.

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AutoIt is standard for Windows sysadmins?

Basically this is a little disagreement and difference between me and my fellow sysadmin colleague.

I write my scripts using Windows batch/command files, vbscript, or Powershell. If I get run over by a bus, the next Windows sysadmin can take over my scripts and see what I did.

Enter my co-worker, who is a very bright guy. He writes everything in AutoIt. He likes to compile them and make .exe files. If he gets hit by a bus, then ...? Sure, he could leave behind the source code somewhere, but should I really be learning AutoIT? Seems like another thing to learn that isn't standardized? He has a disdain for Powershell and vbscripting so he doesn't write in them. I haven't felt the need to even use AutoIT or look at it since I've been able to do everything without it.

Is this the 'use whatever tool works' method, even if this disregards other people? We're supposed to back each other up so being unified would be nice.

EDIT: Thanks for all the feedback and shared experiences with AutoIt. I will try to get him to include source code with his compiled AutoIt scripts.