AS-REP Roasting

Configuring

Prerequisite

pagePassword spraying

Configuring

1. Login on DC02 with the username Administrator and password Welcome01!.

2. Open the "Active Directory Users and Computers" administration tool on DC02.

3. Click on "View" and enable "Advanced Features".

4. Open "Users", right click the user banktest and click on "Properties"

5. Open "Account" and scroll to the bottom in "Account options", then select "Do not require kerberos preauthentication".

6. Click on "Apply" and "OK".

Attacking

How it works

When pre-authentication is not required, an attack can directly send a request for authentication. The KDC will return an encrypted TGT and the attacker can extract the hash and brute-force it offline.

Tools

• Crackmapexec

Executing the attack

AS-REP roasting was already covered in the Initial Access Attacks section.

pageAS-REP Roasting

But since we have a set of valid credentials of the domain now, we could request a list of all usernames and check for AS-REP roastable users. During the Initial Access AS-REP Roasting we used a example script from Impacket. But there are more tools that can accomplish the same thing, such as Crackmapexec.

1. Use the discovered credentials john and password Welcome2022! with crackmapexec to authenticate over ldap and AS-REP roast all roastable users.

crackmapexec ldap 10.0.0.3 -u john -p Welcome2022! --asreproast asreproast.txt

2. We retrieved two hashes, one new one from bankuser. Lets crack it with hashcat and use the passwordlist we created earlier during the passwordspray. The hashcat parameters are:

• Crackingmode: -a 0 for using a wordlist

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

• List with hashes: asreproasting.txt

• Passwords list: passwords.txt

hashcat -a 0 -m 18200 asreproast.txt passwords.txt

We successfully cracked the password of the user bankuser, the password is Bank2022!.

Defending

Recommendations

• Periodically check for users that don't require pre-authentication and remove the attribute.

Check for users with the attribute:

Get-ADUser -Filter {DoesNotRequirePreAuth -eq $true} | Select-Object samAccountName

Remove the attribute for a single user:

Set-ADAccountControl -DoesNotRequirePreAuth $false -Identity <USER>

Check for users with the attribute and remove it:

Get-ADUser -Filter {DoesNotRequirePreAuth -eq $true} | Set-ADAccountControl -DoesNotRequirePreAuth $false

• If pre authenticatio is required. Use strong passwords (at least 32 characters).

Detection

References

GitHub - byt3bl33d3r/CrackMapExec: A swiss army knife for pentesting networksGitHub