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Managing Security in Windows 7 : User Account Control

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User Account Control (UAC) provides an added layer of security to ensure that you are notified if changes to your system are attempted. UAC is intertwined with much of the underlying operations of Windows 7, but the core goal is to limit the capabilities of malicious software.

When a regular user logs on, an access token is created that includes the user's SID and the SIDs of any groups where the user is a member.

In earlier Windows systems, a significant risk was present if a user logged on with administrative permissions. If a system was infected with malware while a user was logged on with administrative permissions, the malware had administrative permissions and was able to do significant damage.

Corporate environments often implemented policies requiring administrators to use two accounts. One account was for regular usage. If administrative access was needed to perform tasks, only the administrative account was used, but only for the time needed to perform the task.

In Windows XP and Windows Server 2003, administrators were able to log on as a regular user and then use the Run As feature to run individual applications with administrative permissions. This reduced the risk of malware taking over the administrative account.

Windows Vista introduced UAC, and Windows 7 has improved on the functionality of UAC. The core goal remains to protect the system from malware that tries to modify settings. UAC requires any attempts to modify the system settings by an application to be approved.

The default UAC setting in Windows 7 separates the actions taken by the user from the actions taken by applications. In other words, if a user makes the change, they aren't prompted by UAC. If an application attempts to make a change, UAC does prompt for approval. This prevents malware from making unauthorized changes while reducing the number of UAC pop-ups when a user is making changes.

NOTE

In Windows Vista, UAC prompted the user every time an action needed administrative privileges. This included every time an application tried to make a change and every time the user tried to make a change. This resulted in a significant number of UAC prompts and was one of the criticisms of Windows Vista.

UAC works by implementing something called Admin Approval Mode. Admin Approval Mode uses two access tokens when a user logs on to Windows 7 with an administrative account. One is for regular use, and the second is used only when administrative permissions are needed.


Standard user access token

This is the token used for most regular work, such as launching and using applications. This token does not have any administrative privileges.


Administrator access token

If an action requires administrative privileges, this token is used. UAC usually prompts the user to use this access token before the token is used.

Figure 1 shows the UAC screen that appears when the administrator access token is needed. The program name identifies the program that is requiring the elevated permissions. In the figure, the command prompt is being launched with administrative permissions.

Figure 1. User Account Control settings screen

Control Panel includes an icon of a shield for any activity that requires UAC permissions. When you click one of these links, the UAC prompt will appear unless the default behavior has been modified.


A useful tool that shows you the different privileges that are available when the administrative token is used is the whoami command-line command. It can be used to get user name and group information along with assigned privileges or rights.

The whoami command is also a quick way to determine the logon context of a user. When entered without a switch, it identifies the user in the format of computer\username or domain\username.


As an example, if a regular user account is used, whoami will show that only the following privileges are assigned:

  • SeShutdownPrivilege shuts down the system.

  • SeChangeNotifyPrivilege bypasses traverse checking.

  • SeUndockPrivilege removes the computer from the docking station.

  • SeIncreaseWorkingSetPrivilege increases a process working set.

  • SeTimeZonePrivilege changes the time zone.

If the administrative account is used, there are over 20 privileges granted.

Exercise 1 shows how to use whoami and, more specifically, allows you easily to see the difference in the privileges assigned to the regular user and the administrator accounts.

Exercise: Using Whoami to View Privileges

  1. Log on to Windows 7 with an account that has administrative permissions but is not the Administrator account.

    (If you log on with the Administrator account, the command prompt will always be launched with administrative privileges and you won't be able to see the differences.)

  2. Launch a command prompt by clicking Start, typing cmd in the Start Search box, and pressing Enter.

  3. Enter the following command:

    Whoami /all

    You can see details on the user account and group memberships. Notice that the BUILTIN\Administrators account is included, but the attribute specifies that this account is being used for Deny Only. In other words, rights and permissions are not being granted for this group. View the list of privileges listed at the end of the output. Leave this command-prompt window open.

  4. Launch a command prompt with elevated permissions. Click Start, type cmd in the Start Search box, right-click cmd, and select Run As Administrator. If prompted by UAC, click Yes.

  5. Enter the following command:

    Whoami /all

    Compare this output to that generated by whoami for the regular user account. The Administrator group isn't being restricted to Deny Only, and the list of privileges is extensive.


1.1. UAC Settings

Although the default setting for UAC provides good protection, you can modify the default behavior. You can access the UAC settings screen by clicking Start, entering UAC in the Start Search box, and pressing Enter. You can also access it by clicking Start => Control Panel => System And Security => Action Center => Change User Account Control Settings.

Figure 2 shows the User Account Control Settings screen with the default settings selected.

Figure 2. User Account Control Settings screen


Always Notify

This is the way that UAC works in Windows Vista. UAC will notify you anytime you make changes to a Windows setting or a program tries to install software or make changes. This level of notification was annoying to many Windows Vista users and was one of the more common complaints. However, for users who routinely install new software and visit unfamiliar websites, it is recommended.


Default – Notify Me Only

When Programs Try To Make Changes To My Computer This setting will still notify you if an application makes changes to your system, but it doesn't notify you when you make changes to Windows settings. This is recommended if you use familiar programs and visit familiar websites.


Notify Me Only When Programs Try To Make Changes To My Computer (Do Not Dim My Desktop)

This setting is similar to the default setting, but it does add some risk. Normally the desktop is dimmed, preventing any action other than addressing the prompt. This setting doesn't dim the desktop. It may allow malware to interfere or dismiss the UAC prompt. This is not recommended.


Never Notify

This setting disables UAC. It is not recommended and is only included for programs that must run in Windows 7 but do not support User Account Control.

NOTE

The dimmed desktop is also referred to as the secure desktop. When the desktop is dimmed, UAC doesn't allow any other actions except for a response to the UAC.

1.2. Configuring UAC via Group Policy

Group Policy includes several settings that you can use to modify the default behavior of UAC. The primary settings you'll modify are located in the Computer Configuration => Policies => Windows Settings => Security Settings => Local Policies => Security Options node.

NOTE

These settings can also be found in the Local Computer Policy in the Computer Configuration => Windows Settings => Security Settings => Local Policies => Security Options node.

The following list explains some of these Group Policy settings:


User Account Control: Run All Administrators In Admin Approval Mode

This setting turns on Admin Approval Mode for all administrators including the Built-in Administrator account. When this setting is disabled, all UAC policy settings are disabled for administrators.


User Account Control: Admin Approval Mode For The Built-in Administrator Account

This setting affects only users logged on using the built-in Administrator account, not users in the Administrators group. When it is enabled, users who log in using the Administrator account will be prompted by UAC. This setting is disabled by default, meaning that anyone logged in with the local Administrator account will not be prompted by UAC. The administrator access token will be used by default whenever it is needed.


User Account Control: Behavior Of The Elevation For Administrators In Admin Approval Mode

This setting affects any user in the local Administrators group when Admin Approval Mode is enabled. When enabled it has several possible settings:

  • Elevate Without Prompting

  • Prompt For Credentials On The Secure Desktop

  • Prompt For Consent On The Secure Desktop

  • Prompt For Credentials

  • Prompt For Consent

  • Prompt For Consent For Non-Windows Binaries (Default)


User Account Control: Behavior Of The Elevation Prompt For Standard Users

If users are logged on with standard user accounts (non-administrator accounts), you can use this setting to control what happens if they try to do something that requires elevated permissions. The three choices are as follows:

  • Prompt For Credentials On The Secure Desktop (Default)

  • Prompt For Credentials

  • Automatically Deny Elevation Requests


User Account Control: Switch To The Secure Desktop When Prompting For Elevation

If enabled, this setting overrides other settings and ensures that all UAC requests dim the desktop for administrators and standard users.


User Account Control: Detect Application Installations And Prompt For Elevation

This setting is disabled by default for computers joined to a domain. When disabled, it allows applications to be deployed via Group Policy or advanced tools such as Systems Management Server (SMS) or Systems Center Configuration Manager (SCCM).


User Account Control: Only Elevate Executables That Are Signed And Validated

When this setting is enabled, only files that are signed with a certificate and can be verified via a certification authority are permitted to run. This setting is disabled by default.


User Account Control: Virtualize File And Registry Write Failures To Per-User Locations

This setting allows some legacy applications still to operate in Windows 7. UAC prevents applications from writing data to protected locations and the application fails. However, enabling this setting allows the write failures to be redirected to user locations when the application runs. The application can still operate, but the data is stored in the user profile instead of modifying the system.

Other -----------------
- Group Policy Settings (part 3) - Searching Group Policy
- Group Policy Settings (part 2) - Deploying an Application via Group Policy & AppLocker
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- Group Policy and the GPMC (part 3) - Advanced Group Policy Settings
- Group Policy and the GPMC (part 2) - RSAT and the Group Policy Management Console
- Group Policy and the GPMC (part 1) - Enabling a GPO Setting & Applying Multiple GPOs
- Managing Windows 7 in a Domain : Anti-Malware Software
- Managing Windows 7 in a Domain : Understanding User Profiles (part 2)
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