# AD CS Account Persistence
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**This is a small summary of the machine persistence chapters of the awesome research from [https://www.specterops.io/assets/resources/Certified\_Pre-Owned.pdf](https://www.specterops.io/assets/resources/Certified\_Pre-Owned.pdf)**
## **Understanding Active User Credential Theft with Certificates – PERSIST1**
In a scenario where a certificate that allows domain authentication can be requested by a user, an attacker has the opportunity to **request** and **steal** this certificate to **maintain persistence** on a network. By default, the `User` template in Active Directory allows such requests, though it may sometimes be disabled.
Using a tool named [**Certify**](https://github.com/GhostPack/Certify), one can search for valid certificates that enable persistent access:
```bash
Certify.exe find /clientauth
```
It's highlighted that a certificate's power lies in its ability to **authenticate as the user** it belongs to, regardless of any password changes, as long as the certificate remains **valid**.
Certificates can be requested through a graphical interface using `certmgr.msc` or through the command line with `certreq.exe`. With **Certify**, the process to request a certificate is simplified as follows:
```bash
Certify.exe request /ca:CA-SERVER\CA-NAME /template:TEMPLATE-NAME
```
Upon successful request, a certificate along with its private key is generated in `.pem` format. To convert this into a `.pfx` file, which is usable on Windows systems, the following command is utilized:
```bash
openssl pkcs12 -in cert.pem -keyex -CSP "Microsoft Enhanced Cryptographic Provider v1.0" -export -out cert.pfx
```
The `.pfx` file can then be uploaded to a target system and used with a tool called [**Rubeus**](https://github.com/GhostPack/Rubeus) to request a Ticket Granting Ticket (TGT) for the user, extending the attacker's access for as long as the certificate is **valid** (typically one year):
```bash
Rubeus.exe asktgt /user:harmj0y /certificate:C:\Temp\cert.pfx /password:CertPass!
```
An important warning is shared about how this technique, combined with another method outlined in the **THEFT5** section, allows an attacker to persistently obtain an account’s **NTLM hash** without interacting with the Local Security Authority Subsystem Service (LSASS), and from a non-elevated context, providing a stealthier method for long-term credential theft.
## **Gaining Machine Persistence with Certificates - PERSIST2**
Another method involves enrolling a compromised system’s machine account for a certificate, utilizing the default `Machine` template which allows such actions. If an attacker gains elevated privileges on a system, they can use the **SYSTEM** account to request certificates, providing a form of **persistence**:
```bash
Certify.exe request /ca:dc.theshire.local/theshire-DC-CA /template:Machine /machine
```
This access enables the attacker to authenticate to **Kerberos** as the machine account and utilize **S4U2Self** to obtain Kerberos service tickets for any service on the host, effectively granting the attacker persistent access to the machine.
## **Extending Persistence Through Certificate Renewal - PERSIST3**
The final method discussed involves leveraging the **validity** and **renewal periods** of certificate templates. By **renewing** a certificate before its expiration, an attacker can maintain authentication to Active Directory without the need for additional ticket enrolments, which could leave traces on the Certificate Authority (CA) server.
This approach allows for an **extended persistence** method, minimizing the risk of detection through fewer interactions with the CA server and avoiding the generation of artifacts that could alert administrators to the intrusion.
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