killchain-compendium/Cryptography/Active Directory/Active Directory Certificate Service.md

## Active Directory Certificate Service ADCS

* Internal CA
* PKI
* File system encryption
* Digital signatures
* User authentication

* __Certificates will not be revoked after account password reset__

## Certificate Templates

* Extended/Enhanced Key Usage (EKU)
* Parameter combination can be exploited
* User Certificates may be requested from a member of a Domain User Group
* Machine Certifcates may be requested from a host of a Domain Computer Group 

### Enumeration

* [PSPKIAudit](https://github.com/GhostPack/PSPKIAudit)

```sh
certutil -v -template > ct.txt
```

Exploitable templates should have the following traits:
* `Allow Enroll` or `Allow Full Control` permissions to request certificate
    * Find groups by `net user <username> /domain` --> `Domain Users`, `Domain Computers`
* Client authentication EKU for Kerberos authentication --> `Client Authentication`
* Permission to subject alternative name (SAN), e.g. URL to encrypt. Used to create Kerberos ticket, --> `CT_FLAG_ENROLLEE_SUPPLIES_SUBJECT`
 
### Certificate Creation

* `Win+R` --> `mmc` --> `File` --> `Add/Remove Snap-in` --> `Certificates` (Request Certificate if administration account --> Computer Account)
* After that in the main menu, `Certificates` --> right click on `Personal` --> `All Tasks` --> `Request Certificates` --> `Next` --> `Next` --> `More information is required to enroll this certificate` --> `Common Name` --> `CN=concerto` && `User Principal Name` is the user to impersonate --> `OK` --> select `User Request` --> `Enroll`
* After that in the main menu, `Personal` --> `Certificates` --> __The certificate__
* Right click certificate --> `All Tasks` --> `Export` --> `Yes, export private key` --> `PFX` --> set `Password` --> Save

* An alternative is certipy-ad

### Impersonation 

* Request TGT with the created cert
* Grab TGT

* On the machine via
```sh
Rubeus.exe asktgt /user:<user (UPN) of cert> /enctype:aes256 /certificate:<path to certificate> /password:<certificate file password> /outfile:<name of file to write TGT to.kirbi> /domain:<domain name> /dc:<IP of domain controller>
```
* Select a domain admin via opening `Active Directory Users and Computers`
```sh
.\Rubeus.exe changepw /ticket:<ticketfilename> /new:<new password> /dc:<domain of controller> /targetuser:<domain>\<dauser>
```
* `runas /user:<domain>\<username of DA> cmd.exe`

* Alternatively, load the outfile of rubeus via mimikatz to authenticate as the impersonated user on a remote domain
```sh
privilege::debug
kerberos::ptt <name of file to write TGT to.kirbi>
exit
dir \\<domain>\<dir>$\
```

## CVE-2022-26923

* Aims on abusing templates configuration, the Subject Alternative Name `SAN`. Set it to someone with higher permissions
* User and Machine certificate templates
* User Principal Name is used for `SAN`, this template can not be modified in a way to escalate privileges
* Computer accounts DNS name is used for `SAN`
* Users of the Authenticated Users Group can create 10 Machine Certificates
* __DNS hostname__ is used for authentication
* __Service Principal Names (SPN)__, associates a service logon with a service instance. SPNs are unique
* Permissions of interest, all two are needed
    * Validate write to DNS hostname allows to update DNS hostname of AD object associated with the host
    * Validate write to SPN, update SPN of the AD object associated with the host

### Usage

* User account has to be compromised, use it to enrol a new host on the domain
* Alter the DNS hostname attribute of the AD Object to one of a Domain Controller or other higher privilege
* Remove the SPN attribute to bypass the unique SPN
* With the default template request the machine cert
* authenticate via Kerberos with the template as the higher privileged machine