Windows Credentials Protections

Credentials Protections

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WDigest

The protocol, introduced with Windows XP, is designed for authentication via the HTTP Protocol and is enabled by default on Windows XP through Windows 8.0 and Windows Server 2003 to Windows Server 2012. This default setting results in plain-text password storage in LSASS (Local Security Authority Subsystem Service). An attacker can use Mimikatz to extract these credentials by executing:

sekurlsa::wdigest

To toggle this feature off or on, the UseLogonCredential and Negotiate registry keys within HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\SecurityProviders\WDigest must be set to "1". If these keys are absent or set to "0", WDigest is disabled:

reg query HKLM\SYSTEM\CurrentControlSet\Control\SecurityProviders\WDigest /v UseLogonCredential

LSA Protection

Starting with Windows 8.1, Microsoft enhanced the security of LSA to block unauthorized memory reads or code injections by untrusted processes. This enhancement hinders the typical functioning of commands like mimikatz.exe sekurlsa:logonpasswords. To enable this enhanced protection, the RunAsPPL value in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\LSA should be adjusted to 1:

reg query HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\LSA /v RunAsPPL

Bypass

It is possible to bypass this protection using Mimikatz driver mimidrv.sys:

Credential Guard

Credential Guard, a feature exclusive to Windows 10 (Enterprise and Education editions), enhances the security of machine credentials using Virtual Secure Mode (VSM) and Virtualization Based Security (VBS). It leverages CPU virtualization extensions to isolate key processes within a protected memory space, away from the main operating system's reach. This isolation ensures that even the kernel cannot access the memory in VSM, effectively safeguarding credentials from attacks like pass-the-hash. The Local Security Authority (LSA) operates within this secure environment as a trustlet, while the LSASS process in the main OS acts merely as a communicator with the VSM's LSA.

By default, Credential Guard is not active and requires manual activation within an organization. It's critical for enhancing security against tools like Mimikatz, which are hindered in their ability to extract credentials. However, vulnerabilities can still be exploited through the addition of custom Security Support Providers (SSP) to capture credentials in clear text during login attempts.

To verify Credential Guard's activation status, the registry key LsaCfgFlags under HKLM\System\CurrentControlSet\Control\LSA can be inspected. A value of "1" indicates activation with UEFI lock, "2" without lock, and "0" denotes it is not enabled. This registry check, while a strong indicator, is not the sole step for enabling Credential Guard. Detailed guidance and a PowerShell script for enabling this feature are available online.

reg query HKLM\System\CurrentControlSet\Control\LSA /v LsaCfgFlags

RDP RestrictedAdmin Mode

Traditionally, when connecting to a remote computer via RDP, your credentials are stored on the target machine. This poses a significant security risk, especially when using accounts with elevated privileges. However, with the introduction of Restricted Admin mode, this risk is substantially reduced.

When initiating an RDP connection using the command mstsc.exe /RestrictedAdmin, authentication to the remote computer is performed without storing your credentials on it. This approach ensures that, in the event of a malware infection or if a malicious user gains access to the remote server, your credentials are not compromised, as they are not stored on the server.

It's important to note that in Restricted Admin mode, attempts to access network resources from the RDP session will not use your personal credentials; instead, the machine's identity is used.

This feature marks a significant step forward in securing remote desktop connections and protecting sensitive information from being exposed in case of a security breach.

Cached Credentials

Windows secures domain credentials through the Local Security Authority (LSA), supporting logon processes with security protocols like Kerberos and NTLM. A key feature of Windows is its capability to cache the last ten domain logins to ensure users can still access their computers even if the domain controller is offline—a boon for laptop users often away from their company's network.

The number of cached logins is adjustable via a specific registry key or group policy. To view or change this setting, the following command is utilized:

reg query "HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT\WINDOWS NT\CURRENTVERSION\WINLOGON" /v CACHEDLOGONSCOUNT

Access to these cached credentials is tightly controlled, with only the SYSTEM account having the necessary permissions to view them. Administrators needing to access this information must do so with SYSTEM user privileges. The credentials are stored at: HKEY_LOCAL_MACHINE\SECURITY\Cache

Mimikatz can be employed to extract these cached credentials using the command lsadump::cache.

Protected Users

Membership in the Protected Users group introduces several security enhancements for users, ensuring higher levels of protection against credential theft and misuse:

Credential Delegation (CredSSP): Even if the Group Policy setting for Allow delegating default credentials is enabled, plain text credentials of Protected Users will not be cached.
Windows Digest: Starting from Windows 8.1 and Windows Server 2012 R2, the system will not cache plain text credentials of Protected Users, regardless of the Windows Digest status.
NTLM: The system will not cache Protected Users' plain text credentials or NT one-way functions (NTOWF).
Kerberos: For Protected Users, Kerberos authentication will not generate DES or RC4 keys, nor will it cache plain text credentials or long-term keys beyond the initial Ticket-Granting Ticket (TGT) acquisition.
Offline Sign-In: Protected Users will not have a cached verifier created at sign-in or unlock, meaning offline sign-in is not supported for these accounts.

These protections are activated the moment a user, who is a member of the Protected Users group, signs into the device. This ensures that critical security measures are in place to safeguard against various methods of credential compromise.

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Windows Server 2012, Windows Server 2008 R2, Windows Server 2008

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Last updated 7 months ago