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System Auditing

Before you can begin to track audited events, you must enable auditing on the system itself. As with the other security options configured in this chapter, Terminal Server auditing should be enabled through a group policy object in the active directory. Alternatively you can configure the audit settings directly from the Local Security Settings application, but any options configured in the domain will override this. Figure 16.26 shows the Audit Policy folder containing the available policy properties, which are located in

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

Figure 16.26Figure 16.26 Audit policy settings for Terminal Servers should be defined in a GPO in the active directory.

The auditable events listed in the Audit Policy folder are described in the following list. Unless otherwise stated, these policies are not enabled for either Windows 2000 or Windows 2003 Terminal Server.

  • 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.

Auditing introduces additional performance overhead, so unless you are willing to actively monitor your audit logs and feel their use is necessary, you can provide a performance gain by not implementing auditing. Of course, the performance gains must be worth not having the auditing information available for review if necessary. I suggested some events to audit, but the ones you implement will depend on the information you're interested in tracking and what you feel is necessary. You should monitor your security logs carefully to see if there is extraneous information that can be eliminated.

NOTE

If the Shutdown command has not been removed from the Start menu using a group policy, do not be too surprised if you see restart and shutdown attempt failures made on your Terminal Servers shortly after you implement the new infrastructure. If your users have had previous experience with Windows, they may be accustomed to shutting down their computers when they finish working for the day. This will be common among users who use the Alt+F4 key combination to terminate Windows. Even on a Terminal Server, using Alt+F4 presents the user with the Windows Security dialog box where he or she has the option to shut down. Although regular users will have insufficient privileges to successfully complete this operation, the shutdown or restart attempt still will be logged.

File System Auditing

After enabling object access auditing, you can set up the desired file system auditing. If object access is not being audited (see the preceding section regarding system auditing), any file auditing you configure will simply be ignored. File auditing is enabled by following these steps:

  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."

Figure 16.27Figure 16.27 File and folder auditing options for Windows 2000 and Windows 2003.

Table 16.10 lists my suggested auditing settings for the system and application volumes on a Windows 2000/2003 Terminal Server. On the system volume, you may want to create separate audit settings for the profile directory (%SystemDrive%\Documents and Settings"), since users will continuously be writing, editing, and deleting information from that location.

Table 16.10 Suggested Windows 2000/2003 Terminal Server System and Application Volume Auditing Settings

Volume

Permission

Audit Setting

System/Application

Create Files/Write Data

Failure

 

Create Folders/Append Data

Failure

 

Delete Subfolders and Files

Success, Failure

 

Delete

Success, Failure

 

Change Permissions

Success, Failure

 

Take Ownership

Success, Failure


Registry Auditing

Typically, registry auditing is enabled only on the HKEY_LOCAL_MACHINE hive and all subkeys. The auditable events are set similar to those shown in Figure 16.28.

Figure 16.28Figure 16.28 Registry auditing options for Windows 2000 and Windows 2003.

Registry auditing is enabled through the registry-editing tool (REGEDT32 on Windows 2000, REGEDIT on Windows 2003). Depending on the operating system, the Auditing dialog box is accessed as follows:

  • 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.

Click the Add button to add the users or groups and then select the events to audit. You will need to select the Reset Auditing Entries check box to configure all child objects and enable propagation of inheritable audit entries.

You may receive a message indicating that all subkeys could not be updated. This is okay, as the update process will fail to update subkeys for which you don't have access, such as the HKLM\SECURITY or the HKLM\SAM\SAM key. Auditing on the relevant keys will be updated properly.

You shouldn't monitor success of either the Query event or the Enumerate Subkeys event, because both generate a large number of event entries very quickly and should be enabled only when attempting to troubleshoot or resolve a specific issue.

Connection Auditing

Both versions of Windows support connection auditing, which monitors actions that one user session performs against another or performs directly on the connection configuration. Actions such as modifying connection properties or remotely controlling a user's session can be monitored when connection auditing has been enabled. Figure 16.29 shows the Auditing dialog box for an RDP-TCP connection entry. The selected entries also represent my recommendations for the events to audit. Connection auditing simply tracks the success or failure of performing a particular connection action.

Figure 16.29Figure 16.29 A connection auditing example for the RDP-TCP protocol.

Connection auditing is enabled as follows:

  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.

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