/win10-secure-baseline-gpo

Windows 10 and Server 2016 Secure Baseline Group Policy

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Windows 10 and Server 2016 Secure Baseline GPO

This GPO contains security settings and administrative policies that should apply by default to all domain and standalone (via Local Computer Policy) Windows 10 and Server 2016 computers. These settings aim to provide maximum privacy, security, and performance (in that order), with minimum network communication. Security features that send data to Microsoft, such as SmartScreen, are disabled. The following network traffic is allowed, everything else should be blocked:

  • Network Connectivity Status Indicator (NCSI) tests (see Notes below).
  • Windows updates.
  • Root CA updates.
  • Defender definition updates.
  • Storage Health (Disk Failure Prediction Model) updates.

Use a separate GPO to override settings as needed! Do not use for site-specific configuration! This policy should apply to any Windows system, especially laptops that get connected to insecure networks. Edit only to improve privacy, security, and performance, or to disable non-essential features added in new Windows releases.

This GPO overrides most, but not all, settings in the Default Domain [Controllers] Policy. It also contains unmanaged (preference-type) registry settings that are not disabled when the GPO goes out of scope. Use filters to identify. Some of these settings are not covered by any ADMX template (see LGPO section below).

Installation

Local Computer Policy

Run install.cmd. See LGPO documentation (in Tools) for more info.

Use parse.cmd and build.cmd to convert Registry.pol files to LGPO text format and back. Use sort.cmd to sort entries in LGPO text files for easier diffs. Registry.pol files are usually sorted by keys, but not by values. This makes it difficult to track changes. Sorting LGPO text files and rebuilding Registry.pol files ensures that all entries are always in the same order.

ADMX templates for the local computer are in C:\Windows\PolicyDefinitions. To update existing files in this directory, you must change the owner to Administrators and replace owner on all subcontainers and objects. However, doing this makes sfc unhappy! It's safer to leave existing templates alone and only add missing ones.

If you do change the owner, open advanced security settings again, remove all non-inherited permissions, enable inheritance, and replace all child permissions. Finally, copy the PolicyDefinitions directory from the repository, overwriting all existing files. To fix SFC, run:

dism /online /cleanup-image /restorehealth
sfc /scannow

DISM requires working NCSI (see notes below) or you'll get error 0x800f0906. Since the templates are only required to edit the policy, it's better to just leave them alone. Do a clean Windows install in a VM when a new version is released and update the policy there instead of messing with local templates.

Domain

  1. Copy PolicyDefinitions directory to \\<domain>\SYSVOL\<domain>\Policies\. If this directory already exists, delete or rename it first.
  2. Create a blank GPO using Group Policy Management Console.
  3. Right-click on the new GPO and go through the "Import Settings..." wizard using the GPO directory as the backup source.

Required ADMX templates

These are contained in the PolicyDefinitions directory:

  • Windows 10 and Server 2016 (1607)
  • Windows 10 Fall Creators Update (1709)
  • MSS (Legacy) from Windows 10 and Server 2016 Security Baseline (1709)
  • Windows Restricted Traffic Limited Functionality Baseline (1709)

When an update is released, the entire PolicyDefinitions directory should be rebuilt by copying templates over in the listed order. Copying updated ADMX/ADML files without removing old ones first may cause problems.

Notes

  • Domain Level Account Policies (Password Policy, Account Lockout Policy, and Kerberos Policy) only apply if the GPO is linked at the domain level.
  • Local Administrator is disabled and renamed to LocalAdmin. The password must be set before it can be enabled. Otherwise, you'll get error 7016 in gpresult /h report along with "Security has requested to process its policy settings again" message.
  • Do not disable "Microsoft Account Sign-in Assistant" (aka "wlidsvc") service as suggested by the Restricted Traffic Baseline. Doing so results in error 0x80070426 when running Windows Update.
  • Disabling active Network Connectivity Status Indicator (NCSI) tests breaks Windows Update (0x800704cf), DISM (0x800f0906 or 0x800f081f), and probably other things. Passive-only configuration doesn't fix this, so best to leave both passive and active tests enabled. Windows Update error only happens once if Windows was installed without any network connectivity. After a single successful update, disabling NCSI doesn't seem to cause further problems, but DISM will still run into errors. Guess how many days it took to figure this out.
  • Everything related to Microsoft accounts, Store, Windows Apps, cloud, feedback, and customer spying experience improvement is disabled. Some of these settings are only supported by Enterprise and Education editions.
  • Some functions that are only relevant to domain environments, like dynamic DNS updates, app virtualization, remote printing, etc., are disabled.
  • NTFS 8dot3name creation is disabled for all volumes. Existing short names can be stripped manually (e.g. fsutil 8dot3name strip /s C:), though it's safer to leave them alone for a new installation.
  • NTP client is configured to use pool.ntp.org. Local NTP traffic should be intercepted/redirected by the firewall.
  • "Turn off all Windows spotlight features" policy must be applied within 15 minutes after Windows 10 is installed.

Bugs

  • Denying "Let Windows apps run in the background" right (Windows Components -> App Privacy) breaks Start menu search in v1703.
  • Disabling "Allow Extensions" in Microsoft Edge settings prevents Edge from starting for the first time in v1709. If Edge is started manually, the window closes immediately. If Edge is started by opening an html file, you get "The remote procedure call failed" error message. This does not happen on subsequent launches, so just allow extensions temporarily when starting Edge for the first time.

Suggestions to implement in a separate GPO

  • Automatic Windows updates
  • Interactive logon: Machine inactivity limit
  • Disable UAC on servers
  • Firewall rules and logging (intentionally left unconfigured to allow local management on standalone systems)
  • PKI
  • Redirect NCSI DNS/HTTP tests to your own server
  • Dynamic DNS updates
  • Allow Print Spooler to accept client connections
  • Power settings
  • Reduce some of the IE 11 & Edge restrictions (these policies were set with the assumption that Firefox, Chrome, or another browser is the user's default, and IE/Edge is used only on servers or as an occasional backup)
  • Remote Shell access

LGPO

Tools\LGPO.exe was used to set the following unmanaged registry settings not covered by any ADMX template. This allows the settings to apply via Local Computer Policy, which does not support Preferences (without hacks).

; Disable shared experiences
User
Software\Microsoft\Windows\CurrentVersion\CDP
RomeSdkChannelUserAuthzPolicy
DWORD:0

; Do not hide extensions for known file types
User
Software\Microsoft\Windows\CurrentVersion\Explorer\Advanced
HideFileExt
DWORD:0

; Disable automatic proxy detection
User
Software\Microsoft\Windows\CurrentVersion\Internet Settings
AutoDetect
DWORD:0

Updating policy

Update files under GPO\{07BDCD6A-3F72-473C-82B9-67BB69DBE54D}\DomainSysvol\GPO by copying new versions either from a backup or directly from the policy directory (\\<domain>\SYSVOL\<domain>\Policies\{<GUID>} for domains or %SystemRoot%\System32\GroupPolicy for local computer policy). When Registry.pol files are updated, run parse && sort && build to update LGPO text files and sort entry order.

GPO backups contain a lot of domain-specific information, which has been removed from the XML files in this repository. Therefore, creating a new backup and overwriting all files in the GPO directory is a bad idea. Also, the XML parser used by the import wizard is horrible. Adding a new line in the wrong place causes mmc.exe to crash, so the XML files are a mess.

Domain policies store client-side extension (CSE) GUIDs in LDAP. The CSEs must be updated manually in Backup.xml in order for the policy to be imported and processed correctly. Create a separate backup using the Group Policy Management Console and copy MachineExtensionGuids and UserExtensionGuids elements from there.

Local computer policy stores CSEs in %SystemRoot%\System32\GroupPolicy\GPT.INI. LGPO.exe can be used to enable CSEs via the /e option, but it does not distinguish between machine and user CSEs, which is annoying, and has other problems that are noted below. Therefore, local CSEs are enabled by copying over a pre-configured GPT.INI file.

Keep Backup.xml and GPT.INI files synchronized!

Refreshing CSEs

If you configure and then unconfigure a setting that requires a CSE, that CSE remains enabled, which may slow down policy processing. You can check which CSEs are enabled by generating a report via gpresult /h GPReport.html, and looking at "Extensions Configured" under Computer/User Details -> Group Policy Objects.

To get rid of unnecessary CSEs, create a new GPO (or clear out the local computer policy), and copy all policy files from the repository into the new GPO. For local computer policy, run Tools\LGPO.exe /g GPO, but do not copy GPT.INI. This will preserve all settings in gpedit, but all CSEs will remain disabled.

To re-enable required CSEs:

  1. Open gpedit and filter Administrative Templates to show only configured settings (set Managed and Commented to "Any" and clear all checkboxes).
  2. Open "All Settings" container and double-click on the first setting.
  3. For each setting, toggle Enabled/Disabled via Alt-E and Alt-D shortcuts, which will force gpedit to re-apply it, and then go to the next setting via Alt-N.
  4. Repeat for all user settings.
  5. Finally, toggle one policy under Security Settings and another one under Advanced Audit Policy Configuration.

There are two important caveats when doing this:

  1. If you go too fast, you may run into the following error: "The process cannot access the file because it is being used by another process. (Exception from HRESULT: 0x80070020)." Just repeat the operation for the current setting and keep going. Gpedit uses separate threads to commit changes and these threads get in each other's way sometimes.
  2. Some settings that show up as disabled, but have extra options, must actually be enabled! For example, "Allow Cloud Search" can be disabled, or enabled with the extra option set to "Disable Cloud Search". If you do the latter and then re-open the setting, it will show up as disabled. However, if you compare LGPO text exports of the resulting Registry.pol files, you'll notice that disabling the setting manually causes the associated value (SpynetReporting) to be deleted, whereas enabling it and setting the option to "Disable Cloud Search" sets the value to DWORD:0, which is what we want. If you find any of this confusing, I personally like to imagine myself slowly strangling the people who designed and implemented this stuff. Try it... It's very therapeutic. Here's a (possibly incomplete) list of such settings:
    • Allow Cloud Search
    • Join Microsoft MAPS
    • Limit Enhanced diagnostic data to the minimum required by Windows Analytics

The following table describes all CSE GUIDs referenced by this GPO:

GUID Description
{169EBF44-942F-4C43-87CE-13C93996EBBE} UE-V
{29BBE2D5-DE47-4855-97D7-2745E166DC6D} Cortana search
{2BFCC077-22D2-48DE-BDE1-2F618D9B476D} App-V
{2D4156A2-897A-11DB-BA21-001185AD2B89} Network List Manager Policies MMC snap-in
{35378EAC-683F-11D2-A89A-00C04FBBCFA2} Registry settings
{7933F41E-56F8-41D6-A31C-4148A711EE93} Windows search
{803E14A0-B4FB-11D0-A0D0-00A0C90F574B} Security settings MMC snap-in
{827D319E-6EAC-11D2-A4EA-00C04F79F83A} Security (domain-only)
{C631DF4C-088F-4156-B058-4375F0853CD8} Offline files
{CDEAFC3D-948D-49DD-AB12-E578BA4AF7AA} TCP/IP
{D02B1F72-3407-48AE-BA88-E8213C6761F1} Computer setting
{D02B1F73-3407-48AE-BA88-E8213C6761F1} User setting
{DF3DC19F-F72C-4030-940E-4C2A65A6B612} No idea
[{F3CCC681-B74C-4060-9F26-CD84525DCA2A}{0F3F3735-573D-9804-99E4-AB2A69BA5FD4}] Advanced audit policy configuration

LGPO.exe /e audit does not add the same GUID pair for Advanced Audit Policy Configuration as gpedit. The value above is added by gpedit to gPCMachineExtensionNames (only), whereas LGPO v2.2 adds [{F3CCC681-B74C-4060-9F26-CD84525DCA2A}{DF3DC19F-F72C-4030-940E-4C2A65A6B612}] to both gPCMachineExtensionNames and gPCUserExtensionNames. This is probably not correct, and is another reason to avoid LGPO's CSE handling.

References