1. Divide the server’s storage into at least two logical drives. For my discussions in this chapter I assume that the server drives are X: for the system drive and Y: for the application drive.



2. When assigning permissions, restrict access to read-only and then grant or revoke permissions as required. When Permission Compatibility has been set to Full Security, as just discussed, the file system for the most part is already secure. There is one major change required on a Windows 2000 Terminal Server, which is discussed later in this section.



3. Script security changes so they’re reproducible. File permission changes can be easily scripted using the CACLS command line file security utility that is included with both Windows 2000 and 2003.



4. Be certain to implement all file security prior to installing any applications onto the Terminal Server. I discuss suggested default security settings for the application drive immediately after the system drive discussion. Security-related issues with application installation and execution are discussed in more detail in Chapter 21, "Application Integration."

• Administrators (Full Control)
• SYSTEM (Full Control)
• Users (Read)

@ECHO OFF
ECHO Setting security permissions on system volume. Please wait...

REM ** Grant local Administrators and SYSTEM Full Control
REM ** Grant local Users READ access to the root of the system
volume.

CACLS X:\ /c /g Administrators:F SYSTEM:F Users:R

• Administrators (Full Control)
• SYSTEM (Full Control)
• Users (Read)

@ECHO OFF
ECHO Setting security permissions on application volume. Please
wait...

REM ** Grant local Administrators and SYSTEM Full Control
REM ** Grant local Users READ access to the entire volume.
REM ** Permissions should be adjusted on specific applications if
necessary.

CACLS Y:\ /T /c /g Administrators:F SYSTEM:F Users:R
ECHO y|CACLS Y:\* /T /c /g Administrators:F SYSTEM:F Users:R

REM ** Application-specific changes should be appended below.

• Restricting application access — The most common method of access management is to assume that all Terminal Server users have access to all applications on the server, and only those applications that require limited access are restricted through special application security groups.
       This implementation is commonly used simply because this is the default behavior of Windows. When an application is installed on a Windows Terminal Server, by default it is accessible to all users unless access restrictions are defined at the file system level, the application level, or both. For example, an inventory management system may be installed on a Terminal Server and all users can launch the application and reach the logon prompt, but only those users authorized to actually access the application have a valid user ID and password.
• Granting application access — The alternate application access method assumes that users have no access to any of the applications on the server unless such access has been explicitly granted. Not only is this management method the more restrictive of the two, but it also takes much more work up front to configure properly and can quickly become cumbersome, particularly when a large number of applications are involved. One benefit to being so restrictive is that users are not automatically able to run new applications introduced onto the server; this as a result helps guard against rogue applications being introduced via e-mail or download.

• The "Run only allowed Windows Applications" group policy object. This GPO allows you to manage a list of allowed Windows applications that can be executed by users affected by the policy. Usually the policy is applied to all nonadministrative users logged on to a Terminal Server. The one limitation of this policy is that it does not track applications based on their full path, only their application name. This creates the situation where a user could execute any desired application, simply by changing the application’s name to be the same as an application that is authorized to run.
• The APPSEC security utility. This tool, available as part of the Windows 2000 Server Resource Kit allows you to define a list of allowed applications, much like the "Run only allowed Windows Applications" group policy. The three main differences between this utility and the GPO are:



• All non-administrator users are affected by this application’s restrictions. There is no way to limit the access based on a particular security group.
• Only application executables that reside on a server’s physical drive can be executed. Any attempt to launch a network-based executable will fail.
• The listed applications must reside with the specific path specified for that application. Attempting to run a listed application from any other location will fail.

• Windows Server 2003 does not support the APPSEC security utility. Instead it has introduced the "Software restriction policies," a much more robust version of the "Run only allowed Windows Applications" GPO. This GPO allows for the following:



• Determine whether the default behavior of the GPO is to allow applications to execute based on the access rights of the user, or to restrict access to all executables regardless of access rights.
• Applications to be allowed or restricted can be identified by a binary hash that is calculated, a certificate or a file system path or Internet security zone. These choices allowing for the clear identification of the authorized executable while still allow flexibility in how it is located and run.
• Entire folders can also be managed, allowing all applications within those folders to be assigned restricted or unrestricted application execution access.

User Configuration\Administrative Templates\System

Windows Settings\Security Settings\Software Restriction Policies

• Only one SRP is created for each GPO. After selecting New Software Restriction Policies, that option will no longer be available unless the existing SRP is deleted.
• Under the Software Restriction Policies folder, there are three attributes, which are



• Enforcement — This setting dictates the general enforcement criteria for the policy. By default, it will restrict only executables (not executable libraries such as DLLs) and will apply to all users affected by the policy, including administrators./li>
• Designated File Types — In addition to the standard executables files with the suffix EXE all of the file types listed here are assumed to represent executables and will be included in the software restrictions. File types can be added and removed on this screen./li>
• Trusted Publishers — Defines whether or not the user has any control over what publishers will be trusted when presented with certificates that verify the authenticity of an application.


• The Security Levels folder has two items, Disallowed and Unrestricted. Only one of these items can be set as the default at any given time. When Disallowed is chosen, the policy enforces that no users will be able to run software, unless the software has been designed as an additional rule, which is discussed next. If the Unrestricted option is chosen, then all applications are accessible unless explicitly denied in the Additional Rules section.
• The Additional Rules folder is where the majority of the items will be managed. The purpose of this folder is to store either specific entries that are unrestricted or disallowed. Entries are added here simply by right-clicking and choosing the rule to define the entry. The four choices are Certificate Rule, Hash Rule, Internet Zone Rule and Path Rule. The most common select is Path Rule, allowing an administrator to provide an explicit path to a folder, executable file, or registry location. The security level for the rule dictates if the entry is unrestricted or disallowed.

Computer Configuration\Windows Settings\Security Settings\Local Policies\

• Audit Account Logon Events — This audit policy should not be confused with the Audit Logon Events policy described later in this list. The purpose of this policy is to log an event whenever an account on the computer being configured is used to authenticate on this or any other computer. This option is typically enabled only on a domain controller and is not normally required on a Terminal Server. Windows Server 2003 has this option set to SUCCESS by default on all member servers.
• Audit Account Management — The result of a creation, deletion, or modification of a local user account or group is logged when this audit event is selected. I recommend tracking both success and failure.
• Audit Directory Service Access — Access to an active directory object that has its own system access control list (SACL) is audited using this policy. This audit policy is valid on only a domain controller and so does not need to be set on a Terminal Server. A group policy object is an example of an object in an active directory that has its own SACL.
• Audit Logon Events — Whenever a user attempts to log on or log off the Terminal Server, an event is written to the log. This differs from the Audit Account Logon Events policy, which generates a log entry on the server where the user account resides. The Audit Logon Events policy generates a log entry on the server where the logon was attempted. I recommend that you audit both success and failure. Successful logons let you audit the logon activities for users, and failures may indicate an attempt by someone to access a restricted resource. MetaFrame includes a command line tool called AUDITLOG, which generates output from the security event log based on the logon/logoff information in the security log. See Appendix B, "MetaFrame Presentation Server Command Reference," for more information on this. This event is enabled and set to track SUCCESS events on Windows 2003. It is not defined for Windows 2000.
• Audit Object Access — Access to standard objects that have their own SACL defined, such as files, folders, printers, or the registry, are audited using this policy. I recommend auditing failures since this will indicate users with insufficient privileges attempting to access a resource. Mapping successes offers little value except in isolated situations, because users can successfully access a large number of objects during a single Terminal Server session.
• Audit Policy Change — This setting covers any changes made to the security policies, which are composed of the user rights policies and the audit policies on a Terminal Server. Because of the sensitive nature of this security information and the fact that it should rarely change, both success and failure should always be audited.
• Audit Privilege Use — This audits use of a user right on the Terminal Server, such as taking ownership of an object or changing the system time. Failure should be tracked for this policy.
• Audit Process Tracking — This policy tracks actions such as process (including program) starting and stopping. Indirect object access would include tracking a process or thread from an application that manipulated an object in some way. Failures should normally be audited for this policy.
• Audit System Events — When a user attempts to restart or shut down a system, this policy is triggered. Any event that affects the system security or the security log is also tracked with this event. I recommend auditing both success and failure.

1. Right-click a file object (drive, folder, or file) and select Properties.



2. Click the Security tab and then the Advanced button.



3. Here you find the Auditing tab. By clicking the Add button, you can add groups or users that will be audited based on the options you select. Figure 16.27 shows the auditing options available for both Windows 2000 and 2003, which correspond to the file system security attributes. More information on these specific attributes can be found in Appendix E, "File System and Registry Security Primer."

• Windows 2000: Open REGEDT32, select the Permissions menu, click the Advanced button, and select the Auditing tab.
• Windows 2003: Open REGEDIT, choose Permissions from the Edit menu, click the Advanced button, and select the Auditing tab.

1. Open the Terminal Services Configuration tool located under Administrative Tools on the Start menu.



2. Right-click desired connection protocol (RDP or ICA) and select Properties.



3. From the Permissions tab, click the Advanced button and then select the Auditing tab, where you are presented with the familiar Audit dialog box.