Fine-Grained Password Policies

Active Directory domains in Windows 2000 and Windows Server 2003 permitted only a single password and account lockout policy, defined at the domain level. If an organization wanted different password policy settings for a specified group of users, an administrator had to create a new domain or use a third-party custom password filter. Windows Server 2008 introduces the concept of fine-grained password policies, which enable you to apply granular password and account lockout policy settings to different sets of users within the same domain. For example, you can apply stricter policy settings to accounts associated with users who have access to classified or restricted information, such as legal and product research departments. At the same time, you can maintain more relaxed settings for accounts of other users where these types of information are not available.

To configure a fine-grained password policy, you must be a member of the Domain Admins group, and the domain functional level must be set to Windows Server 2008. You can also delegate control of the task to other users if required.

Fine-grained password policies are stored in AD DS by means of two new object classes that are defined in the schema:

• Password Settings Container— Created by default under the domain’s System container, the Password Settings Container stores the password settings objects (PSO) for the domain.

• Password Settings Object— Holds attributes for all the password policy and account lockout policy settings, as defined earlier in this section. It also contains a multivalued link attribute that links the PSO to users or groups, and an integer precedence value that resolves conflicts if multiple PSOs are applied to the same user or group.

You can link a PSO to a user, global security group, or InetOrgPerson object that is in the same domain. Note that if you link a PSO to a distribution group or a group with a different scope, the PSO is ignored. If multiple PSOs are linked to a single user or group because of membership in multiple groups, only one PSO can be applied; settings cannot be merged between PSOs.

Password Settings Precedence

If more than one PSO is linked to a user or group, the PSO that applies is determined by the precedence attribute, which is associated with each PSO and has an integer value of 1 or greater. The lower the precedence attribute, the higher the priority of a given PSO; for example, a PSO with a precedence value of 3 overrides another PSO with a precedence value of 5.

The following rules determine the resultant PSO that is applied to a user or group when multiple PSOs are present:

• If a PSO is directly linked to the user object, it prevails. Should more than one PSO be linked directly to the user, the PSO with the lowest precedence value prevails, and a warning message is logged to the event log.

• If no PSO is linked directly to the user object, all PSOs applied to the user according to membership in global security groups are evaluated, and the PSO with the lowest precedence value prevails. If more than one PSO with the same precedence value is present, the PSO that is obtained first is used.

• If no PSO is linked to either the user object or any global security groups it is a member of, the settings in the Default Domain Policy GPO are applied.

Configuring Fine-Grained Password Policies

As already stated, you must be a member of the Domain Admins group to create and manage PSOs. You can use the ADSI Edit utility to configure a fine-grained password policy. This involves specifying values for all the Password Policy and Account Lockout Policy settings described earlier in this chapter. This tool was introduced in Chapter 4, “Configuring Additional Active Directory Roles.” Perform the following steps:

1.	Click Start, Run, type adsiedit.msc, and then press Enter.
2.	If the domain name is not visible in the console tree, right-click ADSI Edit and choose Connect To. If Default Naming Context and your domain name are visible in the Connection Settings dialog box, accept them. Otherwise, type the fully qualified domain name (FQDN) of your domain. Then click OK.
3.	Expand your domain name to locate the CN=System container, and then expand this container to locate the CN=Password Settings Container object.
4.	Select this container to display any PSOs that are configured in the domain in the Details pane.
5.	Right-click this container and choose New, Object. This starts a wizard that enables you to define your PSO.
6.	In the Create Object dialog box, the msDS-PasswordSettings object class is the only available class. Ensure that it is selected, and then click Next.
7.	Provide a descriptive value for your PSO, as shown in Figure 7.4, and then click Next. Figure 7.4. Provide a descriptive value that helps you to identify the PSO later.
8.	Type a value for the Password Settings Precedence, and then click Next.
9.	For Password Reversible Encryption Status for User Accounts, type False unless you need reversible encryption, and then click Next.
10.	Type a value for the password history length, and then click Next.
11.	To require password complexity, type True, and then click Next.
12.	Specify a minimum password length, and then click Next.
13.	For the Minimum Password Age for User Accounts value, type a value in the format days:hours:minutes:seconds (for example, 1:00:00:00), and then click Next.
14.	Type a value for Maximum Password Age for User Accounts in the same format, and then click Next.
15.	Type a value for the lockout threshold (number of incorrect passwords before account locks out), and then click Next.
16.	Type a value for the lockout observation window (time for resetting lockout counter) in the same format as already described (for example, 00:00:30:00 for 30 minutes), and then click Next.
17.	Type a value for the lockout duration in the same format, and then click Next.
18.	If you want to define additional optional attributes, click More Attributes. Otherwise, click Finish to complete the creation of the PSO.

To apply the PSO to a user or group, proceed as follows:

1.	Open Active Directory Users and Computers and select Advanced Features under the View menu.
2.	In the console tree, expand System, and then select Password Settings Container. This displays the PSO in the Details pane.
3.	Right-click the PSO and choose Properties.
4.	Select the Attribute Editor tab. As shown in Figure 7.5, this tab displays the values of all attributes that have been configured for the PSO, including those set when you created the PSO. Figure 7.5. The Attribute Editor tab of the PSO’s Properties dialog box includes the values of the password and lockout attributes that you configured.
5.	Scroll to select the msDS-PSOAppliesTo attribute, and then click Edit.
6.	On the Multi-valued Distinguished Name With Security Principal Editor dialog box that displays, click Add Windows Account, type the user or group name, and then click OK. As shown in Figure 7.6, the name you added is displayed in this dialog box. You can also add a user or group with its LDAP distinguished name (DN) by clicking the Add DN button. Figure 7.6. Specifying a user or group that will receive the password policy. [View full size image]
7.	Click OK. The security identifier (SID) of the user or group appears in the Value column of the Attribute Editor tab. You can repeat this process as many times as needed to link the PSO to additional users or groups.
8.	Click OK to close the PSO’s Properties dialog box.

Managing Fine-Grained Password Policies

You can perform several additional managerial tasks on your PSO, as follows:

• Editing policy settings— As described in the previous section, access the Attribute Editor tab of the PSO’s Properties dialog box. Select the policy setting to be edited and click Edit. Then specify the desired value in the Editor dialog box that appears.

• Modify the PSO’s precedence value— In the Attribute Editor tab of the PSO’s Properties dialog box, select the msDS-PasswordSettingsPrecedence value, click Edit, and then specify the desired value in the Integer Attribute Editor dialog box that appears.

• Delete the PSO— If you no longer need the PSO, select it in the Details pane of Active Directory Users and Computers and press the Delete key (or right-click it and choose Delete). Click Yes in the confirmation message box that appears. The policy settings for any users or groups employing this PSO revert to the settings in a lower-priority PSO or to the Default Domain Policy GPO if no other PSO exists.

Viewing the Resultant PSO

As already stated, a PSO configured for the user takes priority over one that is configured for a group to which the user belongs, and group-based PSOs are applied according to the precedence value. If you have configured a large number of PSOs, troubleshooting their application can become problematic. To facilitate this process, you can view which PSO is applying to a user or group. Proceed as follows:

1.	In Active Directory Users and Computers, ensure that Advanced Features is selected.
2.	Select the Users container or the OU of the desired user account to display the user account in the Details pane.
3.	Right-click the user account and choose Properties.
4.	Select the Attribute Editor tab, and then click Filter. In the options list that appears, ensure that Show Attributes/Optional and Show Read-Only Attributes/System-Only are checked.
5.	Scroll the attribute list to locate msDS-ResultantPSO. The value of this attribute displays the DN of the effective PSO, as shown in Figure 7.7. If it displays <not set>, the password settings in the Default Domain Policy GPO are in effect for this account. Click View to see the complete DN. Figure 7.7. You can view the effective PSO for a user or group.

For additional information on fine-grained password policies, including some recommended scenarios for applying these policies, refer to “Step-by-Step Guide for Fine-Grained Password and Account Lockout Policy Configuration” in Appendix A. Links in this appendix also provide additional information on the available attributes and their permitted values.