This commit is contained in:
Paolo Matarazzo 2023-08-14 07:38:38 -04:00
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---
ms.date: 08/08/2023
ms.date: 08/14/2023
title: How Windows Defender Credential Guard works
description: Learn how Windows Defender Credential Guard uses virtualization to protect secrets, so that only privileged system software can access them.
ms.topic: conceptual
@ -11,13 +11,6 @@ Kerberos, NTLM, and Credential Manager isolate secrets by using Virtualization-b
For security reasons, the isolated LSA process doesn't host any device drivers. Instead, it only hosts a small subset of operating system binaries that are needed for security and nothing else. All the binaries are signed with a certificate that VBS trusts, and the signatures are validated before launching the file in the protected environment.
When Windows Defender Credential Guard is enabled, NTLMv1, MS-CHAPv2, Digest, and CredSSP can't use the signed-in credentials. Thus, single sign-on doesn't work with these protocols. However, applications can prompt for credentials or use credentials stored in the Windows Vault, which aren't protected by Windows Defender Credential Guard with any of these protocols.
> [!CAUTION]
> It's recommended that valuable credentials, such as the sign-in credentials, aren't used with NTLMv1, MS-CHAPv2, Digest, or CredSSP protocols. If these protocols must be used by domain or Azure AD users, secondary credentials should be provisioned for these use cases.
When Windows Defender Credential Guard is enabled, Kerberos doesn't allow *unconstrained Kerberos delegation* or *DES encryption*, not only for signed-in credentials, but also prompted or saved credentials.
Here's a high-level overview on how the LSA is isolated by using Virtualization-based security:
:::image type="content" source="images/credguard.png" alt-text="Diagram of the Credential Guard architecture.":::
@ -33,13 +26,14 @@ Some ways to store credentials aren't protected by Windows Defender Credential G
- Physical attacks
- Doesn't prevent an attacker with malware on the PC from using the privileges associated with any credential. We recommend using dedicated PCs for high value accounts, such as IT Pros and users with access to high value assets in your organization
- Third-party security packages
- Digest and CredSSP credentials
- When Windows Defender Credential Guard is enabled, neither Digest nor CredSSP have access to users' logon credentials. This implies no Single Sign-On use for these protocols
- When Windows Defender Credential Guard is enabled, NTLMv1, MS-CHAPv2, Digest, and CredSSP can't use the signed-in credentials. Thus, single sign-on doesn't work with these protocols. However, applications can prompt for credentials or use credentials stored in the Windows Vault, which aren't protected by Windows Defender Credential Guard with any of these protocols
> [!CAUTION]
> It's recommended that valuable credentials, such as the sign-in credentials, aren't used with NTLMv1, MS-CHAPv2, Digest, or CredSSP protocols. If these protocols must be used by domain or Azure AD users, secondary credentials should be provisioned for these use cases.
- Supplied credentials for NTLM authentication aren't protected. If a user is prompted for and enters credentials for NTLM authentication, these credentials are vulnerable to be read from LSASS memory. These same credentials are vulnerable to key loggers as well
- Kerberos service tickets aren't protected by Credential Guard, but the Kerberos Ticket Granting Ticket (TGT) is protected
- When Windows Defender Credential Guard is deployed on a VM, Windows Defender Credential Guard protects secrets from attacks inside the VM. However, it doesn't provide protection from privileged system attacks originating from the host
- Windows logon cached password verifiers (commonly called *cached credentials*)
don't qualify as credentials because they can't be presented to another computer for authentication, and can only be used locally to verify credentials. They're stored in the registry on the local computer and provide validation for credentials when a domain-joined computer can't connect to AD DS during user logon. These *cached logons*, or more specifically, *cached domain account information*, can be managed using the security policy setting **Interactive logon: Number of previous logons to cache** if a domain controller isn't available.
- When Windows Defender Credential Guard is enabled, Kerberos doesn't allow *unconstrained Kerberos delegation* or *DES encryption*, not only for signed-in credentials, but also prompted or saved credentials
- When Windows Defender Credential Guard is enabled on a VM, Windows Defender Credential Guard protects secrets from attacks inside the VM. However, it doesn't provide protection from privileged system attacks originating from the host
- Windows logon cached password verifiers (commonly called *cached credentials*) don't qualify as credentials because they can't be presented to another computer for authentication, and can only be used locally to verify credentials. They're stored in the registry on the local computer and provide validation for credentials when a domain-joined computer can't connect to AD DS during user logon. These *cached logons*, or more specifically, *cached domain account information*, can be managed using the security policy setting **Interactive logon: Number of previous logons to cache** if a domain controller isn't available
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