Kerberoasting

Configuring

1. Login to DC01 with the Administrator user and the password Welcome01!.

2. Open PowerShell as administrator and execute the following commands to create a user with the name sa_admin and set a SPN for it:

net user sa_admin Welcome123456! /add
setspn -A MSSQLsvc/DC03:1433 sa_admin

3. Execute the following command to make the user Enterprise Admin and Domain Admin:

Add-ADGroupMember -Identity "Enterprise Admins" -Members sa_admin
Add-ADGroupMember -Identity "Domain Admins" -Members sa_admin

Attacking

How it works

Service principal names (SPNs) are used to uniquely identify each instance of a Windows service. To enable authentication, Kerberos requires that SPNs be associated with at least one service logon account (an account specifically tasked with running a service.

Adversaries possessing a valid Kerberos ticket-granting ticket (TGT) may request one or more Kerberos ticket-granting service (TGS) service tickets for any SPN from a domain controller (DC). Portions of these tickets may be encrypted with the RC4 algorithm, meaning the Kerberos 5 TGS-REP etype 23 hash of the service account associated with the SPN is used as the private key and is thus vulnerable to offline Brute Force attacks that may expose plaintext credentials

Source: https://attack.mitre.org/techniques/T1558/003/

Tools

• GetUserSPNs.py

Executing the attack

1. Use the discovered credentials john and password Welcome2022! with GetUserSPNs.py from Impacket to Kerberoast all roastable users.

python3 /opt/impacket/examples/GetUserSPNs.py 'amsterdam.bank.local/john:Welcome2022!' -dc-ip 10.0.0.2 -target-domain bank.local -outputfile kerberoast.txt
cat kerberoast.txt

2. We retrieved one hash. Lets crack it with Hashcat. The parameters are:

• Crackingmode: -a 0 for using a wordlist

• Hashmode: -m 18200 for Kerberos 5, etype 23, AS-REP

• List with hashes: kerberoasting.txt

• Passwords list: passwords.txt

• Rule list: -r rules.rule

.\hashcat.exe -a 0 -m 13100 .\kerberoast.txt .\wordlists\rockyou.txt -r .\rules\dive.rule

We successfully cracked the password of the user sa_admin, the password is Welcome123456!

Defending

Recommendations

• Use Group Managed Service Accounts or Managed Service Accounts.

• Limit the privileges of Service Accounts.

• Use strong passwords (at least 32 characters) on service accounts.

Detection

References

Steal or Forge Kerberos Tickets: Kerberoasting, Sub-technique T1558.003 - Enterprise | MITRE ATT&CK®attack.mitre.org

Group Managed Service Accounts overviewMicrosoftLearn