Question about UAC

According to < Windows via C/C++ >:

With Windwos Vista, if a user logs on to the system with开发者_Python百科 an account that grants high privileges such as Admin, in addition to the security token corresponding to this privileged account, a filtered token is also created but granted only with the privileges of a Standard User.

I am wondering, if a user logs on to the system with an account that is even less privileged than Standard User, does the system still create some extra filter token for it? I don't think it is necessary and it doesn't make any sense for the system to do that.

Thanks.

The short answer is that unless the user is an administrator, only a single token is present to represent the user.

When a standard user logs on to a computer a new logon session is created and they are presented with a shell application such as Windows Explorer that was created by the system and associated with the user’s newly created logon session by means of a token. This effectively limits what the user can do since Windows Explorer can only run those applications and access those resources that the user’s logon session permits based on the permissions and privileges specified by the token.

When an administrator logs on to a computer things are a little different and this is where Windows Vista (and Windows 7) differs dramatically from previous versions. Although the system creates a new logon session, it creates not one but two different tokens representing the same logon session. The first token grants all the permissions and privileges afforded to the administrator while the second token is a restricted token, sometimes called a filtered token, offering far fewer permissions and privileges. This restricted token offers practically the same capabilities and constraints as would be granted to a standard user. The system then creates the shell application using the restricted token. This means that although the user is logged on as an administrator, applications are by default run with limited permissions and privileges.

When the administrator needs to perform some task that requires additional permissions or privileges not granted to the restricted token, he or she can elect to run an application using the full security context provided by the unrestricted token. What protects the administrator from malicious code is that this elevation to the unrestricted token is only allowed after the administrator has confirmed the desire to use the unrestricted token by means of a secure prompt provided by the system. Malicious code cannot suppress this prompt and thereby gain complete control over the computer without the user’s knowledge.

When the built-in Administrator account logs on to a computer it appears as if it is treated differently to other users that are part of the Administrators group because it doesn’t receive elevation prompts. This is controlled by a group policy setting entitled “User Account Control: Admin Approval Mode for the built-in Administrator account”. Admin approval mode refers to the elevation prompt that requires an administrator to approve the elevation to the unrestricted token. By default this group policy setting is disabled which means that when the built-in Administrator logs on to a computer it only receives a single unrestricted token. If you enable this group policy setting then the built-in Administrator account will receive a new logon session with two tokens just like the other users that are part of the Administrators group.