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SECURITY

Controlling Access to Files and Folders with NTFS Permissions

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NTFS permissions are always evaluated when a file is accessed. NTFS permissions are fairly complex, and to understand their management, you need to understand the following:
  • Basic permissions What the basic permissions are and how they are used

  • Special permissions What the special permissions are and how they are used

  • Ownership What is meant by file ownership and how file ownership is used

  • Inheritance What is meant by inheritance and how inheritance is used

  • Effective permissions How to determine the effective permissions on files

Understanding and Using the Basic Permissions

In Windows Vista, the owner of a file or a folder has the right to allow or deny access to that resource, as do members of the Administrators group and other authorized users. Using Windows Explorer, you can view the currently assigned basic permissions by right-clicking a file or a folder, selecting Properties on the shortcut menu, and then selecting the Security tab in the Properties dialog box.

As shown in Figure 1, the Group Or User Names list shows all the users and groups with permissions set for the selected resource. If you select a user or a group in this list, the assigned permissions are shown in the Permissions For list. If permissions are shaded (unavailable), as shown in the figure, it means they have been inherited from a parent folder.

Image from book
Figure 1: The Security tab shows the currently assigned basic permissions.

Working with and Setting Basic Permissions

All permissions are stored in the file system as part of the access control list (ACL) assigned to a file or a folder. As described in Table 1, six basic permissions are used with folders and five are also used with files. Although some permissions are inherited based on permissions of a parent folder, all permissions are defined explicitly at some level of the file system hierarchy.

Table 1: Basic File and Folder Permissions

Permission

Description

Full Control

Grants the user or group full control over the selected file or folder and permits reading, writing, changing, and deleting files and subfolders. A user with Full Control over a folder can change permissions, delete files in the folder regardless of the permission on the files, and can also take ownership of a folder or a file. Selecting this permission selects all the other permissions as well.

Modify

Allows the user or group to read, write, change, and delete files. A user with Modify permission can also create files and subfolders but cannot take ownership of files. Selecting this permission selects all the permissions below it.

Read & Execute

Permits viewing and listing files and subfolders as well as executing files. If applied to a folder, this permission is inherited by all files and subfolders within the folder. Selecting this permission selects the List Folder Contents and Read permissions as well.

List Folder Contents (folders only)

Similar to the Read & Execute permission but available only for folders. Permits viewing and listing files and subfolders as well as executing files. Unlike Read & Execute, this permission is inherited only by subfolders but not by files within the folder or subfolders.

Read

Allows the user or group to view and list the contents of a folder. A user with this permission can view file attributes, read permissions, and synchronize files. Read is the only permission needed to run scripts. Read access is required to access a shortcut and its target.

Write

Allows the user or group to create new files and write data to existing files. A user with this permission can also view file attributes, read permissions, and synchronize files. Giving a user permission to write to but not delete a file or a folder doesn't prevent the user from deleting the folder or file's contents.

Equally as important as the basic permissions are the users and groups to which you assign those permissions. If a user or a group whose permissions you want to assign is already selected in the Group Or User Names list on the Security tab, you can modify the assigned permissions using the Allow and Deny columns in the Permissions For list. Select check boxes in the Allow column to add permissions, or clear check boxes to remove permissions.

To expressly forbid a user or a group from using a permission, select the appropriate check boxes in the Deny column. Because denied permissions have precedence over other permissions, Deny is useful in two specific scenarios:

  • If a user is a member of a group that has been granted a permission, you don't want the user to have the permission, and you don't want to or can't remove the user from the group, you can override the inherited permission by denying that specific user the right to use the permission.

  • If a permission is inherited from a parent folder and you'd rather a user or a group not have the inherited permission, you can override the allowed permissions (in most cases) by expressly denying the user or group the use of the permissions.

If users or groups whose permissions you want to assign aren't already available in the Group Or User Names list on the Security tab, you can easily add them. To set basic permissions for users or groups not already listed on a file or a folder's Security tab, follow these steps:

  1. On the Security tab, click Edit. This displays the Permissions For dialog box.

  2. In the Permissions For dialog box, click Add to display the Select Users Or Groups dialog box, shown in Figure 2.

    Image from book
    Figure 2: Use Select Users, Computers, or Groups to specify the groups whose permissions you want to configure.


    Tip 

    Always double-check the value of the From This Location field. In workgroups, computers will always only show local accounts and groups. In domains, this field is changeable and set initially to the default (logon) domain of the currently logged on user. If this isn't the location you want to use for selecting user and group accounts to work with, click Locations to see a list of locations you can search, including the current domain, trusted domains, and other resources that you can access.

  3. Type the name of a user or a group account in the selected or default domain. Be sure to reference the user account name rather than a user's full name. When entering multiple names, separate them with semicolons.

  4. Click Check Names. If a single match is found for each entry, the dialog box is automatically updated as appropriate and the entry is underlined. Otherwise, you'll see an additional dialog box. If no matches are found, you've either entered an incorrect name part or you're working with an incorrect location. Modify the name in the Name Not Found dialog box and try again, or click Locations to select a new location. When multiple matches are found, select the name(s) you want to use in the Multiple Names Found dialog box and then click OK. The users and groups are added to the Name list.

  5. You can now configure permissions for each user and group you added by selecting an account name and then allowing or denying access permissions as appropriate.

Special Identities and Best Practices for Assigning Permissions

When you work with basic permissions, it is important to understand not only how the permissions are used but also how special identities can be used to help you assign permissions. The special identities you'll see the most are Creator Owner and Users, but others are also used occasionally, as described in Table 2.

Table 2: Special Identities Used When Setting Permissions

Special Identity

Description

Anonymous Logon

Includes any network logons for which credentials are not provided. This special identity is used to allow anonymous access to resources, such as those available on a Web server.

Authenticated Users

Includes users and computers who log on with a user name and password; does not include users who log on as Guest, even if the Guest account is assigned a password.

Creator/Owner

The special identity for the account that created a file or a folder. Windows Vista uses this group to identify the account that has ultimate authority over the file or folder.

Dialup

Includes any user who accesses the computer with a dial-up connection. This identity is used to distinguish dial-up users from other types of users.

Everyone

Includes all interactive, dial-up, and authenticated users. Although this group includes guests, it does not include anonymous users.

Interactive

Includes any user logged on locally or through a remote desktop connection.

Network

Includes any user who logs on over the network. This identity is used to allow remote users to access a resource and does not include interactive logons that use remote desktop connections.

Users

Includes authenticated users and domain users only. In Windows Vista, the built-in users group is preferred over everyone.

A solid understanding of these special identities can help you more effectively configure permissions on NTFS volumes. Additionally, whenever you work with permissions, you should keep the following guidelines in mind:

  • Follow the file system hierarchy Inheritance plays a big part in how permissions are set. By default, permissions you set on a folder apply to all files and subfolders within that folder. With this in mind, start at the root folder of a local disk or a user's profile folder (both of which act as top-level folders) when you start configuring permissions.

  • Have a plan Don't set permissions without a clear plan. If permissions get out of sync on folders, and you are looking for a way to start over so that you have some continuity, you might want to configure the permissions as they should be in a parent folder and then reset the permissions on all subfolders and files in that folder.

  • Grant access only as necessary An important aspect of the file access controls built into NTFS is that permissions must be explicitly assigned. If you don't grant a permission to a user and that user isn't a member of a group that has a permission, the user doesn't have that permission—it's that simple. When assigning permissions, it is especially important to keep this rule in mind because it's tempting just to give users full control rather than the specific permissions they really need. Granting only the specific permissions users need to do their job is known as the principle of least privilege.

  • Use groups to manage permissions more efficiently Whenever possible, you should make users members of the appropriate groups and then assign permissions to those groups rather than assigning permissions to individual users. In this way, you can grant permissions to new users by making them members of the appropriate groups, and then, when a user leaves or goes to another group, you can change the group membership as appropriate. For example, when Sarah joins the sales team, you can add her to the SalesUS and SalesCan groups so that she can access those groups' shared data. If she later leaves the sales team and joins the marketing team, you can remove her from the SalesUS and SalesCan groups and add her to the MarketingUS and MarketingCan groups. This is much more efficient than editing the properties for every folder Sarah will need access to and assigning permissions.

Assigning Special Permissions

Windows Vista uses special permissions to carefully control the permissions of users and groups. Behind the scenes, whenever you work with basic permissions, Windows Vista manages a set of related special permissions that specify exactly the permitted actions. The special permissions that are applied for each of the basic permissions are as follows:

  • Read

    • q List Folder/Read Data

    • q Read Attributes

    • q Read Extended Attributes

    • q Read Permissions

  • Read & Execute or List Folder Contents

    • q All special permissions for Read listed previously

    • q Traverse Folder/Execute File

  • Write

    • q Create Files/Write Data

    • q Create Folders/Append Data

    • q Write Attributes

    • q Write Extended Attributes

  • Modify

    • q All special permissions for Read listed previously

    • q All special permissions for Write listed previously

    • q Delete

  • Full Control

    • q All special permissions listed previously

    • q Delete Subfolders And Files

    • q Change Permissions

    • q Take Ownership

Table 3 describes how Windows Vista uses each special permission.

Table 3: Special Permissions for Files and Folders

Special Permission

Description

Traverse Folder /Execute File

Traverse Folder allows direct access to a folder in order to reach subfolders, even if you don't have explicit access to read the data it contains. Execute File allows you to run an executable file.

List Folder /Read Data

List Folder lets you view file and folder names. Read Data allows you to view the contents of a file.

Read Attributes

Allows you to read the basic attributes of a file or a folder. These attributes include Read-Only, Hidden, System, and Archive.

Read Extended Attributes

Allows you to view the extended attributes (named data streams) associated with a file.

Create Files /Write Data

Create Files allows you to put new files in a folder. Write Data allows you to overwrite existing data in a file (but not add new data to an existing file, because this is covered by Append Data).

Create Folders /Append Data

Create Folders allows you to create subfolders within folders. Append Data allows you to add data to the end of an existing file (but not to overwrite existing data, because this is covered by Write Data).

Write Attributes

Allows you to change the basic attributes of a file or a folder. These attributes include Read-Only, Hidden, System, and Archive.

Write Extended Attributes

Allows you to change the extended attributes (named data streams) associated with a file.

Delete Subfolders and Files

Allows you to delete the contents of a folder. If you have this permission, you can delete the subfolders and files in a folder even if you don't specifically have Delete permission on the subfolder or the file.

Delete

Allows you to delete a file or a folder. If a folder isn't empty and you don't have Delete permission for one of its files or subfolders, you won't be able to delete it. You can delete a folder that contains other items only if you have Delete Subfolders And Files permission.

Read Permissions

Allows you to read all basic and special permissions assigned to a file or a folder.

Change Permissions

Allows you to change basic and special permissions assigned to a file or a folder.

Take Ownership

Allows you to take ownership of a file or a folder. By default, administrators can always take ownership of a file or a folder and can also grant this permission to others.

In Windows Explorer, you can view special permissions for a file or a folder by right-clicking the file or the folder you want to work with and then selecting Properties. In the Properties dialog box, select the Security tab and then click Advanced to display the Advanced Security Settings dialog box, as shown in Figure 3. In this dialog box, the permissions are presented much as they are on the Security tab. The key differences are that you see individual allow or deny permission sets along with whether and how the permissions are inherited, as well as the resources to which the permissions will apply.

Image from book
Figure 3: Use the Advanced Security Settings dialog box to configure special permissions.

Once you've accessed the Advanced Security Settings dialog box, you can set special permissions using the Add, Edit, and Remove buttons. To add a user or a group and then set special permissions for that user or group, follow these steps:

  1. On the Security tab, click Advanced to display the Advanced Security Settings dialog box.

  2. On the Permissions tab, click Edit. This opens the Advanced Security Settings dialog box for editing.

  3. Click Add. This displays the Select User Or Group dialog box.

  4. Type the name of a user or a group account in the selected or default domain. Be sure to reference the user account name rather than a user's full name. Only one name can be entered at a time.

  5. When you click OK, the Permission Entry For dialog box, shown in Figure 4, is displayed.

    Image from book
    Figure 4: Configure the special permissions that should be allowed or denied.

  6. Allow or deny special permissions as appropriate. If any permissions are shaded (unavailable), they are being inherited from a parent folder. You can override the inherited permission if necessary by selecting the opposite permission, such as Deny rather than Allow.

  7. If the options on the Apply Onto list are available, choose the appropriate options to ensure the permissions are properly inherited. The options include the following:

    • q This Folder Only The permissions will apply only to the currently selected folder.

    • q This Folder, Subfolders And Files The permissions will apply to this folder, any subfolders of this folder, and any files in any of these folders.

    • q This Folder And Subfolders The permissions will apply to this folder and any subfolders of this folder. They will not apply to any files in any of these folders.

    • q This Folder And Files The permissions will apply to this folder and any files in this folder. They will not apply to any subfolders of this folder.

    • q Subfolders And Files Only The permissions will apply to any subfolders of this folder and any files in any of these folders. They will not apply to this folder itself.

    • q Subfolders Only The permissions will apply to any subfolders of this folder but will not apply to the folder itself or any files in any of these folders.

    • q Files Only The permissions will apply to any files in any of these folders and any files in subfolders of this folder. They will not apply to this folder itself or to subfolders.

  8. When you are finished configuring permissions, click OK.

File Ownership and Permission Assignment

The owner of a file or a folder has the right to allow or deny access to that resource. Although members of the Administrators group and other authorized users also have the right to allow or deny access, the owner has the authority to lock out non-administrator users and then the only way to regain access to the resource is for an administrator or restore operator to take ownership of it. This makes the file or folder owner important in terms of what permissions are allowed or denied with respect to a given resource.

The default owner of a file or a folder is the person who created the resource. Ownership can be taken or transferred in several different ways. A current owner of a file or a folder can transfer ownership to another user or group at any time. A member of the Administrators group can take ownership of a file or a folder or transfer ownership to another user or group at any time—even if they are locked out of the resource according to the permissions. Any user with the Take Ownership permission on the file or the folder can take ownership, as can any member of the Backup Operators group (or anyone else with the Restore Files And Directories user right, for that matter).

Taking Ownership of Files and Folders

If you are an administrator, an authorized user, or a backup operator, you can take ownership of a file or a folder by completing the following steps:

  1. In Windows Explorer, access the file or folder's Properties dialog box by right-clicking the file or folder and then selecting Properties.

  2. On the Security tab, click Advanced to display the Advanced Security Settings dialog box.

  3. On the Owner tab, click Edit. This opens the Advanced Security Settings dialog box for editing, as shown in Figure 5.

    Image from book
    Figure 5: Use the Owner tab to take ownership of a file or a folder.

  4. In the Change Owner To list box, select the new owner. If you're taking ownership of a folder, you can take ownership of all subfolders and files within the folder by selecting the Replace Owner On Subcontainers And Objects option.

  5. Click OK twice when you are finished.

Assigning Ownership

If you are an administrator or the current owner of a file, you can assign ownership of a file or a folder to another user or group by completing these steps:

  1. In Windows Explorer, access the file or folder's Properties dialog box by right-clicking the file or folder and then selecting Properties.

  2. On the Security tab, click Advanced to display the Advanced Security Settings dialog box.

  3. On the Owner tab, click Edit. This opens the Advanced Security Settings dialog box for editing.

  4. Click Other Users Or Groups to display the Select User Or Group dialog box.

  5. Type the name of a user or a group and click Check Names. If multiple names match the value you entered, you'll see a list of names and will be able to choose the one you want to use. Otherwise, the name will be filled in for you, and you can click OK to close the Select User Or Group dialog box.

  6. In the Change Owner To list box, select the new owner. If you're assigning ownership of a folder, you can assign ownership of all subfolders and files within the folder by selecting the Replace Owner On Subcontainers And Objects option.

  7. Click OK twice when you are finished.

Applying Permissions Through Inheritance

In the file and folder hierarchy used by Windows Vista, the root folder of a local disk and the %UserProfile% folder are the parent folders of all the files and folders they contain by default. Any time you add a resource, it inherits the permissions of the local disk's root folder or the user's profile folder. You can change this behavior by modifying a folder's inheritance settings so that it no longer inherits permissions from its parent folder. This would create a new parent folder, and any subfolders or files you added would then inherit the permissions of this folder.

Inheritance Essentials

Inheritance is automatic, and inherited permissions are assigned when a file or a folder is created. If you do not want a file or a folder to have the same permissions as a parent, you have several choices:

  • Stop inheriting permissions from the parent folder and then copy or remove existing permissions as appropriate.

  • Access the parent folder and configure the permissions you want all included files and folders to have.

  • Try to override an inherited permission by selecting the opposite permission. In most cases, Deny overrides Allow.

Inherited permissions are shaded (unavailable) on the Security tab of a file or a folder's properties dialog box. It is also important to note that when you assign new permissions to a folder, the permissions propagate down to the subfolders and files contained in that folder and either supplement or replace existing permissions. This propagation lets you allow additional users and groups to access a folder's resources or to further restrict access to a folder's resources independently of a parent folder.

To better understand inheritance, consider the following examples:

  • On drive C, you create a folder named Data and then create a subfolder named CurrentProjects. By default, Data inherits the permissions of the C:\ folder, and these permissions are in turn inherited by the CurrentProjects folder. Any files you add to the C:\, C:\Data, and C:\Data\CurrentProjects folders will have the same permissions—those inherited from the C:\ folder.

  • On drive C, you create a folder named Docs and then create a subfolder named Working. You stop inheritance on the Working folder by removing the inherited permissions of the parent. Any files you add to the C:\Docs\Working folder inherit the permissions of the C:\Docs folder and no other.

  • On drive C, you create a folder named Backup and then create a subfolder named Sales. You add permissions to the Sales folder that grant access to members of the Sales group. Any files added to the C:\Backup\Sales folder inherit the permissions of the C:\ folder and also have additional access permissions for members of the Sales group.


Real World 

Many new administrators wonder what the advantage of inheritance is and why it is used. Although it occasionally seems inheritance is more trouble than it's worth, inheritance enables you to very efficiently manage permissions. Without inheritance, you'd have to configure permissions on every file and folder you created. If you wanted to change permissions later, you'd have to go through all your files and folders again. With inheritance, all new files and folders automatically inherit a set of permissions. If you need to change permissions, you can make the changes in a top-level or parent folder and the changes can be automatically applied to all subfolders and files in that folder. In this way, a single permission set can be applied to many files and folders without editing the security of individual files and folders.

Viewing Inherited Permissions

To view the inherited permissions on a file or a folder, right-click the file or folder in Windows Explorer and then select Properties. On the Security tab of the Properties dialog box, click Advanced to display the Advanced Security Settings dialog box, shown previously in Figure 3. The Permission column lists the current permissions assigned to the resource. If the permission is inherited, the Inherited From column shows the parent folder from which the permission has been inherited. If the permission will be in turn inherited by other resources, the Apply To column shows the types of resources that will inherit the permission.

Stopping Inheritance

If you want a file or a folder to stop inheriting permissions from a parent folder, follow these steps:

  1. In Windows Explorer, right-click the file or folder and then select Properties. On the Security tab, click Advanced.

  2. On the Permissions tab, click Edit. This opens the Advanced Security Settings dialog box for editing.

  3. Clear Include Inheritable Permissions From This Object's Parent.

  4. As shown in Figure 6, you now have the opportunity to copy over the permissions that were previously applied or remove the inherited permissions and apply only the permissions that you explicitly set on the folder or file. Click Copy or Remove as appropriate. Assign additional permissions as necessary.

Image from book
Figure 6: Copy or remove the inherited permissions.

Tip 

If you remove the inherited permissions and there are no other permissions assigned, everyone but the owner of the resource will be denied access. This effectively locks everyone except the owner out of a folder or file. However, administrators still have the right to take ownership of the resource regardless of the permissions. Thus, if an administrator was locked out of a file or a folder and truly needed access, she could take ownership and then have unrestricted access.

Restoring Inherited Permissions

Over time, the permissions on files and subfolders can become so dramatically different from those of a parent folder that it is nearly impossible to effectively manage access. To make it easier to manage file and folder access, you might want to take the drastic step of restoring the inherited permissions to all resources contained in a parent folder. In this way, subfolders and files get all inheritable permissions from the parent folder, and all other explicitly defined permissions on the individual subfolders and files are removed.

To restore the inherited permissions of a parent folder, follow these steps:

  1. In Windows Explorer, right-click the file or folder and then select Properties. On the Security tab, click Advanced.

  2. On the Permissions tab, click Edit. This opens the Advanced Security Settings dialog box for editing.

  3. Select Replace All Existing Inheritable Permissions and click OK.

  4. As shown in Figure 7, you will see a prompt explaining that this action will replace all explicitly defined permissions and enable propagation of inheritable permissions. Click Yes.

Image from book
Figure 7: Click Yes to confirm that you want to replace the existing permissions.

Determining the Effective Permissions and Troubleshooting

NTFS permissions are complex and can be difficult to manage. Sometimes a change—even a very minor one—can have unintended consequences. Users might suddenly find they are denied access to files they could previously access, or they might suddenly find they have access to files to which access should never have been granted. In either scenario, something has gone wrong with permissions. You have a problem, and you need to fix it.

You should start troubleshooting these or other problems with permissions by determining the effective permissions for the files or the folders in question. As the name implies, the effective permissions tell you exactly which permissions are in effect with regard to a particular user or group. The effective permissions are important because they enable you to quickly determine the cumulative set of permissions that apply.

For a user, the effective permissions are based on all the permissions the user has been granted or denied, no matter whether they were applied explicitly or obtained from groups of which the user is a member. For example, if JimB is a member of the Users, Sales, Marketing, SpecTeam, and Managers groups, the effective permissions on a file or a folder would be the cumulative set of permissions that JimB has been explicitly assigned and those permissions assigned to the Users, Sales, Marketing, SpecTeam, and Managers groups.

To determine the effective permissions for a user or a group with regard to a file or a folder, complete the following steps:

  1. In Windows Explorer, right-click the file or folder you want to work with and then select Properties. In the Properties dialog box, select the Security tab and then click Advanced to display the Advanced Security Settings dialog box.

  2. To determine effective permissions that are applied to a user or a group, click the Effective Permissions tab, click Select, type the name of the user or group, and then click OK.

  3. The Effective Permissions for the specified user or group are displayed using the complete set of special permissions. If a user has full control over the selected resource, he or she will have the permissions, as shown in Figure 8. Otherwise, you'll see a subset of permissions selected and you'll have to carefully consider whether the user or group has the appropriate permissions. Use Table 3 to help you interpret the permissions.

Image from book
Figure 8: Any checked permissions have been granted to the specified user or group.

Note 

You must have appropriate permissions to view the effective permissions of any user or group. It is also important to remember that you cannot determine the effective permissions for implicit groups or special identities, such as Authenticated Users or Everyone. Furthermore, the effective permissions do not take into account those permissions granted to a user because he or she is the Creator Owner.

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