Detections
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2.2.8 Ensure 'Change the system time' is set to 'Administrators, LOCAL SERVICE'

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Information

This policy setting determines which users and groups can change the time and date on the internal clock of the computers in your environment.

Users who are assigned this user right can affect the appearance of event logs.

When a computer's time setting is changed, logged events reflect the new time, not the actual time that the events occurred.

The recommended state for this setting is: 'Administrators, LOCAL SERVICE'.

Note: Discrepancies between the time on the local computer and on the Domain Controllers in your environment may cause problems for the Kerberos authentication protocol, which could make it impossible for users to log on to the domain or obtain authorization to access domain resources after they are logged on.

Also, problems will occur when Group Policy is applied to client computers if the system time is not synchronized with the Domain Controllers.

Rationale:
Users who can change the time on a computer could cause several problems.

For example, time stamps on event log entries could be made inaccurate, time stamps on files and folders that are created or modified could be incorrect, and computers that belong to a domain may not be able to authenticate themselves or users who try to log on to the domain from them.

Also, because the Kerberos authentication protocol requires that the requestor and authenticator have their clocks synchronized within an administrator-defined skew period, an attacker who changes a computer's time may cause that computer to be unable to obtain or grant Kerberos tickets.

The risk from these types of events is mitigated on most Domain Controllers, Member Servers, and end-user computers because the Windows Time service automatically synchronizes time with Domain Controllers in the following ways:

- All client desktop computers and Member Servers use the authenticating Domain Controller as their inbound time partner.
- All Domain Controllers in a domain nominate the Primary Domain Controller (PDC) Emulator operations master as their inbound time partner.
- All PDC Emulator operations masters follow the hierarchy of domains in the selection of their inbound time partner.
- The PDC Emulator operations master at the root of the domain is authoritative for the organization.

Therefore it is recommended that you configure this computer to synchronize with a reliable external time server.

This vulnerability becomes much more serious if an attacker is able to change the system time and then stop the Windows Time service or reconfigure it to synchronize with a time server that is not accurate.

Solution

To establish the recommended configuration via GP, set the following UI path to 'Administrators, LOCAL SERVICE':


Computer Configuration\Policies\Windows Settings\Security Settings\Local Policies\User Rights Assignment\Change the system time


Impact:
There should be no impact, because time synchronization for most organizations should be fully automated for all computers that belong to the domain.

Computers that do not belong to the domain should be configured to synchronize with an external source.

See Also

https://workbench.cisecurity.org/files/1929

Item Details

Category: ACCESS CONTROL

References: 800-53|AC-6(7), CSCv6|5.1

Plugin: Windows

Control ID: b9feb2c077c969b38f15b7afd17ec79a53e16a88f27b549dd5236509e68c890a