Enforce password history
Applies To: Windows Vista, Windows Server 2008, Windows 7, Windows 8.1, Windows Server 2008 R2, Windows Server 2012 R2, Windows Server 2012, Windows 8
This security policy reference topic for the IT professional describes the best practices, location, values, policy management, and security considerations for this policy setting.
Reference
The Enforce password history policy setting determines the number of unique new passwords that must be associated with a user account before an old password can be reused.
Password reuse is an important concern in any organization. Many users want to reuse the same password for their account over a long period of time. The longer the same password is used for a particular account, the greater the chance that an attacker will be able to determine the password through brute force attacks. If users are required to change their password, but they can reuse an old password, the effectiveness of a good password policy is greatly reduced.
Specifying a low number for Enforce password history allows users to continually use the same small number of passwords repeatedly. If you do not also set Minimum password age, users can change their password as many times in a row as necessary to reuse their original password.
This policy setting is supported on versions of Windows that are designated in the Applies To list at the beginning of this topic.
Possible values
User-specified number from 0 through 24
Not defined
Best practices
Set Enforce password history to 24. This will help mitigate vulnerabilities that are caused by password reuse.
Set Maximum password age to 60 days. Try to expire the passwords between major business cycles to prevent work loss.
Configure Minimum password age so that you do not allow passwords to be changed immediately.
Location
GPO_name**\Computer Configuration\Windows Settings\Security Settings\Account Policies\Password Policy**
Default values
The following table lists the actual and effective default policy values for the most recent supported versions of Windows. Default values are also listed on the policy’s property page.
Server type or GPO |
Default value |
|---|---|
Default domain policy |
24 passwords remembered |
Default domain controller policy |
Not defined |
Stand-alone server default settings |
0 passwords remembered |
Domain controller effective default settings |
24 passwords remembered |
Member server effective default settings |
24 passwords remembered |
Effective GPO default settings on client computers |
24 passwords remembered |
Operating system version differences
There are no differences in the way this policy setting works between supported versions of Windows.
Policy management
This section describes features, tools, and guidance to help you manage this policy.
Restart requirement
None. Changes to this policy become effective without a computer restart when they are saved locally or distributed through Group Policy.
Security considerations
This section describes how an attacker might exploit a feature or its configuration, how to implement the countermeasure, and the possible negative consequences of countermeasure implementation.
Vulnerability
The longer a user uses the same password, the greater the chance that an attacker can determine the password through brute force attacks. Also, any accounts that may have been compromised remain exploitable for as long as the password is left unchanged. If password changes are required but password reuse is not prevented, or if users continually reuse a small number of passwords, the effectiveness of a good password policy is greatly reduced.
If you specify a low number for this policy setting, users can use the same small number of passwords repeatedly. If you do not also configure the Minimum password age policy setting, users might repeatedly change their passwords until they can reuse their original password.
Note
After an account has been compromised, a simple password reset might not be enough to restrict a malicious user because the malicious user might have modified the user's environment so that the password is changed back to a known value automatically at a certain time. If an account has been compromised, it is best to delete the account and assign the user a new account after all affected systems have been restored to normal operations and verified that they are no longer compromised.
Countermeasure
Configure the Enforce password history policy setting to 24 (the maximum setting) to help minimize the number of vulnerabilities that are caused by password reuse.
For this policy setting to be effective, you should also configure effective values for the Minimum password age and Maximum password age policy settings.
Potential impact
The major impact of configuring the Enforce password history setting to 24 is that users must create a new password every time they are required to change their old one. If users are required to change their passwords to new unique values, there is an increased risk of users who write their passwords somewhere so that they do not forget them. Another risk is that users may create passwords that change incrementally (for example, password01, password02, and so on) to facilitate memorization, but this makes them easier for an attacker to guess. Also, an excessively low value for the Maximum password age policy setting is likely to increase administrative overhead because users who forget their passwords might ask the Help Desk to reset them frequently.