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BP-2510: Add warning about NTLM data collection for protected users group #293

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BP-2510: Add warning about NTLM data collection for protected users group #293

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12 changes: 11 additions & 1 deletion docs/manage-bloodhound/securing-bloodhound-and-collectors/sharphound-hardening.mdx
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Expand Up @@ -27,14 +27,24 @@ Using a gMSA will reduce the risk of having the SharpHound service account compr

Furthermore, using a gMSA makes it possible to have the SharpHound service account in the Protected Users group, which is covered in the following recommendation.

### Protected User group
### Protected Users group

We recommend adding the SharpHound service account as a member of the [Protected Users](https://learn.microsoft.com/en-us/windows-server/security/credentials-protection-and-management/protected-users-security-group) group.

Protected Users is an AD security group designed to reduce credential exposure. Members of this group automatically have non-configurable protections applied to their accounts. Protected Users members cannot be delegated with Kerberos and cannot authenticate using NTLM, effectively remediating Kerberos delegation attacks, NTLM relay attacks, and NTLM cracking. However, Microsoft advises against adding service accounts to the group as authentication for the service account may fail.

Our testing has shown that adding the SharpHound service account to Protected Users works if the SharpHound service account is a gMSA, but the SharpHound service crashes after four hours if it is a regular AD user.

<Warning>
Adding the SharpHound service account to Protected Users also prevents SharpHound from authenticating with NTLM during collection.

This means SharpHound cannot collect the NTLM data from domain controllers and ADCS servers that BloodHound uses to create the following edges:

- [CoerceAndRelayNTLMToLDAP](/resources/edges/coerce-and-relay-ntlm-to-ldap)
- [CoerceAndRelayNTLMToLDAPS](/resources/edges/coerce-and-relay-ntlm-to-ldaps)
- [CoerceAndRelayNTLMToADCS](/resources/edges/coerce-and-relay-ntlm-to-adcs)
</Warning>

### Tiering SharpHound

We recommend tiering the SharpHound service account to follow the principle of "[elevated user accounts should not be used to log on to lower Tier assets](https://techcommunity.microsoft.com/t5/core-infrastructure-and-security/protecting-domain-administrative-credentials/ba-p/259210)".
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