For security compliance purpose, I want to enforce some Windows settings on the Windows server via the group policy. Some GPOs already exist in the domain. Instead of modifying the existing GPOs, I create a new GPO and link it to the OU where the servers locate. I think I can easily roll back / undo the new settings if they cause any issue, by moving the server out of the OU or unlinking the GPO to the OU.
It turns out my original thought is not 100% correct. Some security settings still persist even if the setting is no longer defined in the policy.
For example, on a new Windows Server 2012 R2 server, the local security policy setting of “Network Security: LAN Manager authentication level” is “Not Defined”. In my new GPO, I configure this setting to “Send NTLMv2 response only; Refuse LM & NTLM”. After linking this new GPO to the OU, I cannot RDP to the servers with the domain login (the error message is “The logon attempted failed”, even my username and password are correct), but the local login is okay.
I unlink the new GPO from the OU for troubleshooting and expect the security settings rolling back to their original configuration. However, I get the same error. And the local security policy on the server still configures “Send NTLMv2 response only; Refuse LM & NTLM”. I reset this setting on the local security policy back to the default “Not Defined”. That solves the problem.
Some posts give me the idea on the fix: post 1, post 2.
Now I learn the “tattooing” behavior on the security settings in the GPO.
Persistence in security settings
Security settings may still persist even if a setting is no longer defined in the policy that originally applied it.
Persistence in security settings occurs when:
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The setting has not been previously defined for the computer.
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The setting is for a registry object.
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The setting is for a file system object.
All settings applied through local policy or a Group Policy Object are stored in a local database on your computer. Whenever a security setting is modified, the computer saves the security setting value to the local database, which retains a history of all the settings that have been applied to the computer. If a policy first defines a security setting and then no longer defines that setting, then the setting takes on the previous value in the database. If a previous value does not exist in the database, then the setting does not revert to anything and remains defined as is. This behavior is sometimes called "tattooing."
Registry and file settings will maintain the values applied through policy until that setting is set to other values
Reference: Administer Security Policy Settings, “Persistence in security settings”
