Shadow Credentials

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Intro

Check the original post for all the information about this technique.

As summary: if you can write to the msDS-KeyCredentialLink property of a user/computer, you can retrieve the NT hash of that object.

In the post, a method is outlined for setting up public-private key authentication credentials to acquire a unique Service Ticket that includes the target's NTLM hash. This process involves the encrypted NTLM_SUPPLEMENTAL_CREDENTIAL within the Privilege Attribute Certificate (PAC), which can be decrypted.

Requirements

To apply this technique, certain conditions must be met:

A minimum of one Windows Server 2016 Domain Controller is needed.
The Domain Controller must have a server authentication digital certificate installed.
The Active Directory must be at the Windows Server 2016 Functional Level.
An account with delegated rights to modify the msDS-KeyCredentialLink attribute of the target object is required.

Abuse

The abuse of Key Trust for computer objects encompasses steps beyond obtaining a Ticket Granting Ticket (TGT) and the NTLM hash. The options include:

Creating an RC4 silver ticket to act as privileged users on the intended host.
Using the TGT with S4U2Self for impersonation of privileged users, necessitating alterations to the Service Ticket to add a service class to the service name.

A significant advantage of Key Trust abuse is its limitation to the attacker-generated private key, avoiding delegation to potentially vulnerable accounts and not requiring the creation of a computer account, which could be challenging to remove.

Tools

### Whisker

It's based on DSInternals providing a C# interface for this attack. Whisker and its Python counterpart, pyWhisker, enable manipulation of the msDS-KeyCredentialLink attribute to gain control over Active Directory accounts. These tools support various operations like adding, listing, removing, and clearing key credentials from the target object.

Whisker functions include:

Add: Generates a key pair and adds a key credential.
List: Displays all key credential entries.
Remove: Deletes a specified key credential.
Clear: Erases all key credentials, potentially disrupting legitimate WHfB usage.

Whisker.exe add /target:computername$ /domain:constoso.local /dc:dc1.contoso.local /path:C:\path\to\file.pfx /password:P@ssword1

pyWhisker

It extends Whisker functionality to UNIX-based systems, leveraging Impacket and PyDSInternals for comprehensive exploitation capabilities, including listing, adding, and removing KeyCredentials, as well as importing and exporting them in JSON format.

python3 pywhisker.py -d "domain.local" -u "user1" -p "complexpassword" --target "user2" --action "list"

ShadowSpray

ShadowSpray aims to exploit GenericWrite/GenericAll permissions that wide user groups may have over domain objects to apply ShadowCredentials broadly. It entails logging into the domain, verifying the domain's functional level, enumerating domain objects, and attempting to add KeyCredentials for TGT acquisition and NT hash revelation. Cleanup options and recursive exploitation tactics enhance its utility.

References