Disabling User Account Control (UAC) on Windows Server
- Only administrators are allowed to log on to the Windows-based server interactively at the console or by using Remote Desktop Services.
- Administrators log on to the Windows-based server only to perform legitimate system administrative functions on the server.
- This guidance applies only to Windows Server operating systems such as Windows Server 2008 and Windows Server 2008 R2.
- UAC is always disabled on the Server Core editions of Windows Server 2008 R2 and later versions and should always be kept disabled on Windows Server 2008 Server Core. A hotfix (KB 969371) is available for Windows Server 2008 Server Core to prevent UAC from being enabled accidentally.
- File and Registry Virtualization: When a "legacy" application tries to write to protected areas of the file system or of the registry, Windows silently and transparently redirects the access to a part of the file system or of the registry that the user is allowed to change. This enables many applications that required administrative rights on earlier versions of Windows to run successfully with only standard user rights on Windows Server 2008 and later versions.
- Same-desktop Elevation: When an authorized user runs and elevates a program, the resulting process is granted more powerful rights than those of the interactive desktop user. By combining elevation with UAC's Filtered Token feature (see the following bullet point), administrators can run programs with standard user rights and then elevate only those programs that require administrative rights with the same user account. (This same-user elevation feature is also known as Admin Approval Mode.) Programs can also be started with elevated rights by using a different user account so that an administrator can perform administrative tasks on a standard user's desktop.
- Filtered Token: When a user who has administrative or other powerful privileges or group memberships logs on, Windows creates two access tokens to represent the user account. The "unfiltered" token has all the user's group memberships and privileges, whereas the "filtered" token represents the user with the equivalent of standard user rights. By default, this filtered token is used to run the user's programs. The unfiltered token is associated only with elevated programs. An account that is a member of the Administrators group and that receives a filtered token when the user logs on is called a "Protected Administrator" account.
- User Interface Privilege Isolation (UIPI): UIPI prevents a lower-privileged program from sending window messages such as synthetic mouse or keyboard events to a window that belongs to a higher-privileged process and by doing this controlling the higher-privileged process.
- Protected Mode Internet Explorer (PMIE): PMIE is a defense-in-depth feature in which Windows Internet Explorer operates in low-privileged Protected Mode and cannot write to most areas of the file system or of the registry. By default, Protected Mode is enabled when a user browses sites in the Internet or Restricted Sites zones. PMIE makes it more difficult for malware that infects a running instance of Internet Explorer to change the user's settings, such as by configuring itself to start every time that the user logs on. Be aware that PMIE is not actually part of UAC. However, it depends on UAC features such as UIPI.
- Installer Detection: When a new process is about to be started without administrative rights, Windows applies heuristics to determine whether the new process is likely to be a legacy installation program. Windows assumes that legacy installation programs are likely to fail without administrative rights. Therefore, Windows proactively prompts the interactive user for elevation. Be aware that if the user does not have administrative credentials, the user cannot run the program.
If you disable the User Account Control: Run all administrators in Admin Approval Mode policy setting, this disables all the UAC features that are described in this section. This policy setting is available through the computer's Local Security Policy, Security Settings, Local Policies, and then Security Options. Legacy applications that have standard user rights that expect to write to protected folders or registry keys will fail. Filtered tokens are not created, and all programs run with the full rights of the user who is logged on to the computer. This includes Internet Explorer because Protected Mode is disabled for all security zones.
One of the common misconceptions about UAC and about Same-desktop Elevation in particular is that it prevents malware from being installed or from gaining administrative rights. First, malware can be written not to require administrative rights, and malware can be written to write just to areas in the user's profile. More important, Same-desktop Elevation in UAC is not a security boundary and can be hijacked by unprivileged software that runs on the same desktop. Same-desktop Elevation should be considered a convenience feature, and from a security perspective, "Protected Administrator" should be considered the equivalent of "Administrator." By contrast, using Fast User Switching to log on to a different session by using an administrator account involves a security boundary between the administrator account and the standard user session. For more information about security boundaries, see the "References" section.
For a Windows-based server on which the sole reason for interactive logon is to administer the system, the goal of fewer elevation prompts is neither feasible nor desirable. System administrative tools legitimately require administrative rights. When all the administrative user's tasks require administrative rights and each task could trigger an elevation prompt, the prompts are only a hindrance to productivity. In this context, such prompts do not and cannot promote the goal of encouraging development of applications that require standard user rights. Also, such prompts do not improve the security posture. Instead, these prompts just encourage users to click through dialog boxes without reading them.
Be aware that this guidance applies only to well-managed servers on which only administrative users can log on interactively or through Remote Desktop services, and only to perform legitimate administrative functions. If administrators run risky applications such as web browsers, email clients, or instant messaging clients or perform other operations that should be performed from a client operating system, the server should be considered equivalent to a client system. In this case, UAC should remain enabled as a defense-in-depth measure.
Also, if standard users log on to the server at the console or through Remote Desktop services to run applications, especially web browsers, UAC should remain enabled to support file and registry virtualization and also Protected Mode Internet Explorer.
Another option to avoid elevation prompts without disabling UAC is to set the User Account Control: Behavior of the elevation prompt for administrators in Admin Approval Mode security policy to Elevate without prompting. By using this setting, elevation requests are silently approved if the user is a member of the Administrators group. This option also leaves PMIE and other UAC features enabled. However, not all operations that require administrative rights request elevation. Using this setting can result in some of the user's programs being elevated and some not, without any way to distinguish between them. For example, most console utilities that require administrative rights expect to be started at a command prompt or other program that is already elevated. Such utilities merely fail when they are started at a command prompt that is not elevated.
Additional effects of disabling UAC
- If you try to use Windows Explorer to browse to a directory in which you do not have Read permissions, Explorer will offer to change the directory's permissions to grant your user account access to it permanently. The results depend on whether UAC is enabled. For more information, click the following article number to view the article in the Microsoft Knowledge Base: 950934 When you click Continue for folder access in Windows Explorer, your user account is added to the ACL for the folder
- If UAC is disabled, Windows Explorer continues to display UAC "shield" icons for items that require elevation and to include Run as administrator in the context menus of applications and application shortcuts. Because the UAC elevation mechanism is disabled, these commands have no effect, and applications run in the same security context as the user who is logged on.
- If UAC is enabled, when the console utility Runas.exe is used to start a program by using a user account that is subject to token filtering, the program runs with the user's filtered token. If UAC is disabled, the program that is started runs with the user's full token.
- If UAC is enabled, local accounts that are subject to token filtering cannot be used for remote administration over network interfaces other than Remote Desktop (for example, through NET USE or WinRM). A local account that authenticates over such an interface obtains only the privileges that are granted to the account's filtered token. If UAC is disabled, this restriction is removed. (The restriction can also be removed by using the LocalAccountTokenFilterPolicy setting that is described in Microsoft Knowledge Base article 951016.) Removing this restriction can increase the risk of system compromise in an environment where many systems have an administrative local account that has the same user name and password. We recommend that you make sure that other mitigations are employed against this risk. For more information about recommended mitigations, click the following link:
Artikelnummer: 2526083 – Letzte Überarbeitung: 02/12/2014 03:08:00 – Revision: 7.0