Planning and Deploying Advanced Security Audit Policies

Applies To: Windows HPC Server 2008 R2, Windows 7, Windows 8.1, Windows Server 2012 R2, Windows Server 2012, Windows 8

This topic for the IT professional explains the options that security policy planners must consider and the tasks they must complete to deploy an effective security audit policy in a network that includes Advanced Security Audit policies.

Overview

Organizations invest a large portion of their information technology budgets on security applications and services, such as antivirus software, firewalls, and encryption. But no matter how much security hardware or software you deploy, how tightly you control the rights of users, or how carefully you configure security permissions on your data, you should not consider the job complete unless you have a well-defined, timely auditing strategy to track the effectiveness of your defenses and identify attempts to circumvent them.

To be well defined and timely, an auditing strategy must provide useful tracking data for an organization's most important resources, critical behaviors, and potential risks. In a growing number of organizations, it must also provide absolute proof that IT operations comply with corporate and regulatory requirements.

Unfortunately, no organization has unlimited resources to monitor every resource and activity on a network. If you do not plan well, you will likely have gaps in your auditing strategy. However, if you try to audit every resource and activity, you may find yourself with far too much monitoring data, including thousands of benign audit entries that an analyst needs to sift through to identify the narrow set of entries that warrant closer examination. This could cause delays or even prevent auditors from identifying suspicious activity. Thus, too much monitoring can leave an organization as vulnerable as not enough monitoring.

Auditing features introduced in Windows 7 and Windows Server 2008 R2 made it easier to audit important user, computer, and network activities in a focused, efficient manner. These features include:

• Advanced audit policy settings   Allow administrators to more narrowly apply and manage detailed audit policy settings through their existing Group Policy framework.

• "Reason for access" auditing   Enables administrators to specify and identify the permissions that were used to generate a particular object access security event.

• Global object access auditing   Allows administrators to define system access control lists (SACLs) for an entire computer file system or registry.

To deploy these features and plan an effective security auditing strategy, you need to:

• Identify your most critical resources and the most important activities that need to be tracked.

• Identify the audit settings that can be used to track these activities.

• Assess the advantages and potential costs associated with each.

• Test these settings to validate your choices.

• Develop plans for deploying and managing your audit policy.

About this guide

This document will guide you through the steps needed to plan a security auditing policy that uses Windows auditing features. This policy must identify and address vital business needs, including:

• Network reliability

• Regulatory requirements

• Protection of the organization's data and intellectual property

• Users, including employees, contractors, partners, and customers

• Client computers and applications

• Servers and the applications and services running on those servers

The audit policy also must identify processes for managing audit data after it has been logged, including:

• Collecting, evaluating, and reviewing audit data

• Storing and (if required) disposing of audit data

By carefully planning, designing, testing, and deploying a solution based on your organization's business requirements, you can provide the standardized functionality, security, and management control that your organization needs.

Supported versions of Windows

Basic security audit policy settings

The basic security audit policy settings can be used to log audit events on any computer running any of the supported versions of Windows in addition to Windows Server 2008, Windows Server 2003, Windows 2000 Server, or a computer running Windows Vista, Windows XP, or Windows 2000 that can join a domain.

Advanced audit policy settings

The advanced audit policy settings can be configured and used to log audit events on any computer running any of the supported versions of Windows.

In addition, the advanced audit policy settings can be applied by using a logon script on computers running Windows Vista or Windows Server 2008.

Terminology used in this guide

Understanding the following terms will help you apply the guidance in this document:

• Group Policy. The Windows feature that allows administrators to specify options to manage configurations for groups of computers and users.

• Audit policy. The nine security audit policy settings under Security Settings\Local Policies\Audit Policy and 53 audit policy settings under Security Settings\Advanced Audit Policy Configuration that determine the security events to be recorded in the security event log.

• Success audit. An audit event that is triggered when a defined action, such as accessing a file share, is completed successfully.

• Failure audit. An audit event that is triggered when a defined action, such as a user logon, is not completed successfully.

• System access control lists (SACLs). A section of the security descriptor for objects, which is used to maintain per-object auditing information. For many types of objects, such as file system objects or registry settings, audit events are logged only if the relevant audit policy has been applied to the computer and a corresponding SACL has been configured on the object. However, you can ensure that a system-wide SACL is applied to all file system objects or all registry settings on a computer by using global object access auditing.

• "Reason for access" audit. This list of access control entries (ACEs) provides the rights for which the decision to allow or deny access to the object was based. This can be useful for documenting the permissions, such as group memberships, that allow or prevent the occurrence of a particular auditable event. For more information about using "reason for access" auditing, see the Advanced Security Auditing Walkthrough.

• Global object access auditing. In any of the supported versions of Windows , a computer-wide SACL can be applied to all objects in the file system or to all registry settings. The specified SACL is automatically applied to every object of that type, overriding any other SACLS that are configured for or applied to that object. For more information about using global object access auditing, see the Advanced Security Auditing Walkthrough.

Understanding the security audit policy design process

The process of designing and deploying a Windows security audit policy involves the following tasks, which are described in greater detail throughout this document:

• Identifying your Windows security audit policy deployment goals

  This section helps define the business objectives that will guide your Windows security audit policy. It also helps you define the resources, users, and computers that will be the focus of your security auditing.

• Mapping the security audit policy to groups of users, computers, and resources in your organization

  This section explains how to integrate security audit policy settings with domain Group Policy settings for different groups of users, computers, and resources. In addition, if your network includes multiple versions of Windows client and server operating systems, it also explains when to use basic audit policy settings and when to use advanced security audit policy settings.

• Mapping your security auditing goals to a security audit policy configuration

  This section explains the categories of Windows security auditing settings that are available. It also identifies individual Windows security auditing policy settings that can be of particular value to address auditing scenarios.

• Planning for security audit monitoring and management

  This section helps you plan to collect, analyze, and store Windows audit data. Depending on the number of computers and types of activity that you want to audit, Windows event logs can fill up quickly. In addition, this section explains how auditors can access and aggregate event data from multiple servers and desktop computers. It also explains how to address storage requirements, including how much audit data to store and how it must be stored.

• Deploying the security audit policy

  This section provides recommendations and guidelines for the effective deployment of a Windows security audit policy. Configuring and deploying Windows audit policy settings in a test lab environment can help you confirm that the settings you have selected will produce the type of audit data you need. However, only a carefully staged pilot and incremental deployments based on your domain and organizational unit (OU) structure will enable you to confirm that the audit data you generate can be monitored and that it meets your organization's audit needs.

Identifying your Windows security audit policy deployment goals

A security audit policy must support and be a critical and integrated aspect of an organization's overall security design and framework.

Every organization has a unique set of data and network assets (such as customer and financial data and trade secrets), physical resources (such as desktop computers, portable computers, and servers), and users (which can include various internal groups such as finance and marketing, and external groups such as partners, customers, and anonymous users on the website). Not all of these assets, resources, and users justify the cost of an audit. Your task is to identify which assets, resources, and users provide the strongest justification for the focus of a security audit.

To create your Windows security audit plan, begin by identifying:

• The overall network environment, including the domains, OUs, and security groups.

• The resources on the network, the users of those resources, and how those resources are being used.

• Regulatory requirements.

Network environment

An organization's domain and OU structure provide a fundamental starting point for thinking about how to apply a security audit policy because it likely provides a foundation of Group Policy Objects (GPOs) and logical grouping of resources and activities that you can use to apply the audit settings that you choose. It is also likely that certain portions of your domain and OU structure already provide logical groups of users, resources, and activities that justify the time and resources needed to audit them. For information about how to integrate a security audit policy with your domain and OU structure, see Mapping the security audit policy to groups of users, computers, and resources in your organization later in this document.

In addition to your domain model, you should also find out whether your organization creates and maintains a systematic threat model. A good threat model can help you identify threats to key components in your infrastructure, so you can define and apply audit settings that enhance the organization's ability to identify and counter those threats.

For additional details about how to complete each of these steps and how to prepare a detailed threat model, download the IT Infrastructure Threat Modeling Guide.

Data and resources

For data and resource auditing, you need to identify the most important types of data and resources (such as patient records, accounting data, or marketing plans) that can benefit from the closer monitoring that Windows auditing can provide. Some of these data resources might already be monitored through auditing features in products such as Microsoft SQL Server and Exchange Server. If so, you may want to consider how Windows auditing features can enhance the existing audit strategy. As with the domain and OU structure discussed previously, security auditing should focus on your most critical resources. You also must consider how much audit data you will be able to manage.

You can record if these resources have high business impact, medium business impact, or low business impact, the cost to the organization if these data resources are accessed by unauthorized users, and the risk that this access can pose to the organization. The type of access by users (such as Read, Modify, or Copy) can also pose different levels of risk to an organization.

Increasingly, data access and use is governed by regulations, and a breach can result in severe penalties and a loss in credibility for the organization. If regulatory compliance plays a role in how you manage your data, be sure to also document this information.

The following table provides an example of a resource analysis for an organization.

Users

Many organizations find it useful to classify the types of users they have and base permissions on this classification. This same classification can help you identify which user activities should be the subject of security auditing and the amount of audit data they will generate.

Organizations can create distinctions based on the type of rights and permissions needed by users to perform their jobs. For example, under the classification Administrators, larger organizations might assign local administrator responsibilities for a single computer, for specific applications such as Exchange Server or SQL Server, or for an entire domain. Under Users, permissions and Group Policy settings can apply to as many as all users in an organization or as few as a subset of the employees in a given department.

Also, if your organization is subject to regulatory requirements, user activities such as accessing medical records or financial data may need to be audited to verify that you are complying with these requirements.

To effectively audit user activity, begin by listing the different types of users in your organization and the types of data they need access to—in addition to the data they should not have access to.

Also, if external users can access any of your organization's data, be sure to identify them, including if they belong to a business partner, customer, or general user, the data they have access to, and the permissions they have to access that data.

The following table illustrates an analysis of users on a network. Although our example contains a single column titled "Possible auditing considerations," you may want to create additional columns to differentiate between different types of network activity, such as logon hours and permission use.

Computers

Security and auditing requirements and audit event volume can vary considerably for different types of computers in an organization. These requirements can be based on:

• If the computers are servers, desktop computers, or portable computers.

• The important applications the computers run, such as Exchange Server, SQL Server, or Forefront Identity Manager.

  Note

  If the server applications (including Exchange Server and SQL Server) have audit settings. For more information about auditing in Exchange Server, see the Exchange 2010 Security Guide. For more information about auditing in SQL Server 2008, see Auditing (Database Engine). For SQL Server 2012, see SQL Server Audit (Database Engine).

• The operating system versions.

  Note

  The operating system version determines which auditing options are available and the volume of audit event data.

• The business value of the data.

For example, a web server that is accessed by external users requires different audit settings than a root certification authority (CA) that is never exposed to the public Internet or even to regular users on the organization's network.

The following table illustrates an analysis of computers in an organization.

Regulatory requirements

Many industries and locales have strict and specific requirements for network operations and how resources are protected. In the health care and financial industries, for example, there are strict guidelines for who has access to records and how they are used. Many countries have strict privacy rules. To identify regulatory requirements, work with your organization's legal department and other departments responsible for these requirements. Then consider the security configuration and auditing options that can be used to comply with and verify compliance with these regulations.

For more information, see the System Center Process Pack for IT GRC.

Mapping the security audit policy to groups of users, computers, and resources in your organization

By using Group Policy, you can apply your security audit policy to defined groups of users, computers, and resources. To map a security auditing policy to these defined groups in your organization, you should understand the following considerations for using Group Policy to apply security audit policy settings:

• The policy settings you identify can be applied by using one or more GPOs. To create and edit a GPO, use the Group Policy Management Console (GPMC). By using the GPMC to link a GPO to selected Active Directory sites, domains, and OUs, you apply the policy settings in the GPO to the users and computers in those Active Directory objects. An OU is the lowest-level Active Directory container to which you can assign Group Policy settings.

• For every policy setting that you select, you need to decide whether it should be enforced across the organization, or whether it should apply only to selected users or computers. You can then combine these audit policy settings into GPOs and link them to the appropriate Active Directory containers.

• By default, options set in GPOs that are linked to higher levels of Active Directory sites, domains, and OUs are inherited by all OUs at lower levels. However, a GPO that is linked at a lower level can overwrite inherited policies.

  For example, you might use a domain GPO to assign an organization-wide group of audit settings, but want a certain OU to get a defined group of additional settings. To accomplish this, you can link a second GPO to that specific lower-level OU. Therefore, a logon audit setting that is applied at the OU level will override a conflicting logon audit setting that is applied at the domain level (unless you have taken special steps to apply Group Policy loopback processing).

• Audit policies are computer policies. Therefore, they must be applied through GPOs that are applied to computer OUs, not to user OUs. However, in most cases you can apply audit settings for only specified resources and groups of users by configuring SACLs on the relevant objects. This enables auditing for a security group that contains only the users you specify.

  For example, you could configure a SACL for a folder called Payroll Data on Accounting Server 1. This can audit attempts by members of the Payroll Processors OU to delete objects from this folder. The Object Access\Audit File System audit policy setting applies to Accounting Server 1, but because it requires a corresponding resource SACL, only actions by members of the Payroll Processors OU on the Payroll Data folder generates audit events.

• Advanced security audit policy settings were introduced in Windows Server 2008 R2 or Windows 7 and can be applied to those operating systems designated in the Applies To list at the beginning of this topic. These advanced audit polices can only be applied by using Group Policy.

  Note

  These settings can also be applied to computers running Windows Vista or Windows Server 2008, but with these operating systems you must use logon scripts to apply advanced audit policies. Therefore, consider upgrading computers in high-security OUs first so that you can use Group Policy to apply and manage advanced audit policies to monitor high-value computers and their users.

  Important

  Whether you apply advanced audit policies by using Group Policy or by using logon scripts, do not use both the basic audit policy settings under Local Policies\Audit Policy and the advanced settings under Security Settings\Advanced Audit Policy Configuration. Using both basic and advanced audit policy settings can cause unexpected results in audit reporting. If you use Advanced Audit Policy Configuration settings or use logon scripts (for computers running Windows Vista or Windows Server 2008) to apply advanced audit policies, be sure to enable the Audit: Force audit policy subcategory settings (Windows Vista or later) to override audit policy category settings policy setting under Local Policies\Security Options. This will prevent conflicts between similar settings by forcing basic security auditing to be ignored.

  For more information, see article 921469 in the Microsoft Knowledge Base.

The following are examples of how audit policies can be applied to an organization's OU structure:

• Apply data activity settings to an OU that contains file servers. If your organization has servers that contain particularly sensitive data, consider putting them in a separate OU so that you can configure and apply a more precise audit policy to these servers.

• Apply user activity audit policies to an OU that contains all computers in the organization. If your organization places users in OUs based on the department they work in, consider configuring and applying more detailed security permissions on critical resources that are accessed by employees who work in more sensitive areas, such as network administrators or the legal department.

• Apply network and system activity audit policies to OUs that contain the organization's most critical servers, such as domain controllers, CAs, email servers, or database servers.

For more information about planning and deploying Group Policy, see the Group Policy Planning and Deployment Guide.

Mapping your security auditing goals to a security audit policy configuration

After you identify your security auditing goals, you can begin to map them to a security audit policy configuration. This audit policy configuration must address your most critical security auditing goals, but it also must address your organization's constraints, such as the number of computers that need to be monitored, the number of activities that you want to audit, the number of audit events that your desired audit configuration will generate, and the number of administrators available to analyze and act upon audit data.

To create your audit policy configuration, you need to:

1. Explore all of the audit policy settings that can be used to address your needs.

2. Choose the audit settings that will most effectively address the audit requirements identified in the previous section.

3. Confirm that the settings you choose are compatible with the operating systems running on the computers that you want to monitor.

4. Decide which configuration options (Success, Failure, or both Success and Failure) you want to use for the audit settings.

5. Deploy the audit settings in a lab or test environment to verify that they meet your desired results in terms of volume, supportability, and comprehensiveness. Then deploy the audit settings in a pilot production environment to ensure that your estimates of how much audit data your audit plan will generate are realistic and that you can manage this data.

Exploring audit policy options

Security audit policy settings in the supported versions of Windows can be viewed and configured in the following locations:

• Security Settings\Local Policies\Audit Policy. For more information, see Audit Policy Settings Under Local Policies\Audit Policy.

• Security Settings\Local Policies\Security Options. For more information, see Audit Policy Settings Under Local Policies\Security Options.

• Security Settings\Advanced Audit Policy Configuration. For more information, see Advanced Security Audit Policy Settings.

Choosing audit settings to use

Depending on your goals, different sets of audit settings may be of particular value to you. For example, some settings under Security Settings\Advanced Audit Policy Configuration can be used to monitor the following types of activity:

• Data and resources

• Users

• Network

Data and resource activity

For many organizations, compromising the organization's data resources can cause tremendous financial losses, in addition to lost prestige and legal liability. If your organization has critical data resources that need to be protected against any breach, the following settings can provide extremely valuable monitoring and forensic data:

• Object Access\Audit File Share. This policy setting allows you to track what content was accessed, the source (IP address and port) of the request, and the user account that was used for the access. The volume of event data generated by this setting will vary depending on the number of client computers that attempt to access the file share. On a file server or domain controller, volume may be high due to SYSVOL access by client computers for policy processing. If you do not need to record routine access by client computers that have permissions on the file share, you may want to log audit events only for failed attempts to access the file share.

• Object Access\Audit File System. This policy setting determines whether the operating system audits user attempts to access file system objects. Audit events are only generated for objects (such as files and folders) that have configured SACLs, and only if the type of access requested (such as Write, Read, or Modify) and the account that is making the request match the settings in the SACL.

  If success auditing is enabled, an audit entry is generated each time any account successfully accesses a file system object that has a matching SACL. If failure auditing is enabled, an audit entry is generated each time any user unsuccessfully attempts to access a file system object that has a matching SACL. The amount of audit data generated by the Audit File System policy setting can vary considerably, depending on the number of objects that have been configured to be monitored.

  Note

  To audit user attempts to access all file system objects on a computer, use the Global Object Access Auditing settings Registry (Global Object Access Auditing) or File System (Global Object Access Auditing).

• Object Access\Audit Handle Manipulation. This policy setting determines whether the operating system generates audit events when a handle to an object is opened or closed. Only objects with configured SACLs generate these events, and only if the attempted handle operation matches the SACL.

  Event volume can be high, depending on how SACLs are configured. When used together with the Audit File System or Audit Registry policy settings, the Audit Handle Manipulation policy setting can provide an administrator with useful "reason for access" audit data that details the precise permissions on which the audit event is based. For example, if a file is configured as a Read-only resource but a user attempts to save changes to the file, the audit event will log not only the event, but also the permissions that were used (or attempted to be used) to save the file changes.

• Global Object Access Auditing. A growing number of organizations are using security auditing to comply with regulatory requirements that govern data security and privacy. But demonstrating that strict controls are being enforced can be extremely difficult. To address this issue, the supported versions of Windows include two Global Object Access Auditing policy settings, one for the registry and one for the file system. When you configure these settings, they apply a global system access control SACL on all objects of that class on a system, which cannot be overridden or circumvented.

  Important

  The Global Object Access Auditing policy settings must be configured and applied in conjunction with the Audit File System and Audit Registry audit policy settings in the Object Access category. For more information about using the Global Object Access Auditing policy settings, see the Advanced Security Auditing Walkthrough.

User activity

The settings in the previous section relate to activity involving the files, folders, and network shares that are stored on a network, and the settings in this section focus on the users, including employees, partners, and customers, who may try to access those resources.

In the majority of cases, these attempts will be legitimate and a network needs to make vital data readily available to legitimate users. However in other cases, employees, partners, and others may attempt to access resources that they have no legitimate reason to access. Security auditing can be used to track a wide variety of user activities on a particular computer to diagnose and resolve problems for legitimate users and identify and address illegitimate activities. The following are a few important settings that you should evaluate to track user activity on your network:

• Account Logon\Audit Credential Validation. This is an extremely important policy setting because it enables you to track every successful and unsuccessful attempt to present credentials for a user logon. In particular, a pattern of unsuccessful attempts may indicate that a user or application is using credentials that are no longer valid, or attempting to use a variety of credentials in succession in hope that one of these attempts will eventually be successful. These events occur on the computer that is authoritative for the credentials. For domain accounts, the domain controller is authoritative. For local accounts, the local computer is authoritative.

• Detailed Tracking\Audit Process Creation and Detailed Tracking\Audit Process Termination. These policy settings can enable you to monitor the applications that a user opens and closes on a computer.

• DS Access\Audit Directory Service Access and DS Access\Audit Directory Service Changes. These policy settings provide a detailed audit trail of attempts to access create, modify, delete, move, or undelete objects in Active Directory Domain Services (AD DS). Only domain administrators have permissions to modify AD DS objects, so it is extremely important to identify malicious attempts to modify these objects. In addition, although domain administrators should be among an organization's most trusted employees, the use of Audit Directory Service Access and Audit Directory Service Changes settings allow you to monitor and verify that only approved changes are made to AD DS. These audit events are logged only on domain controllers.

• Logon/Logoff\Audit Account Lockout. Another common security scenario occurs when a user attempts to log on with an account that has been locked out. It is important to identify these events and to determine whether the attempt to use an account that has been locked out is malicious.

• Logon/Logoff\Audit Logoff and Logon/Logoff\Audit Logon. Logon and logoff events are essential to tracking user activity and detecting potential attacks. Logon events are related to the creation of logon sessions, and they occur on the computer that was accessed. For an interactive logon, events are generated on the computer that was logged on to. For network logon, such as accessing a shared resource, events are generated on the computer that hosts the resource that was accessed. Logoff events are generated when logon sessions are terminated.

  Note

  There is no failure event for logoff activity because failed logoffs (such as when a system abruptly shuts down) do not generate an audit record. Logoff events are not 100 percent reliable. For example, the computer can be turned off without a proper logoff and shutdown, and a logoff event is not generated.

• Logon/Logoff\Audit Special Logon. A special logon has administrator-equivalent rights and can be used to elevate a process to a higher level. It is recommended to track these types of logons. For more information about this feature, see article 947223 in the Microsoft Knowledge Base.

• Object Access\Audit Certification Services. This policy setting allows you to track and monitor a wide variety of activities on a computer that hosts Active Directory Certificate Services (AD CS) role services to ensure that only authorized users are performing or attempting to perform these tasks, and that only authorized or desired tasks are being performed.

• Object Access\Audit File System and Object Access\Audit File Share. These policy settings are described in the previous section.

• Object Access\Audit Handle Manipulation. This policy setting and its role in providing "reason for access" audit data is described in the previous section.

• Object Access\Audit Registry. Monitoring for changes to the registry is one of the most critical means that an administrator has to ensure malicious users do not make changes to essential computer settings. Audit events are only generated for objects that have configured SACLs, and only if the type of access that is requested (such as Write, Read, or Modify) and the account making the request match the settings in the SACL.

  Important

  On critical systems where all attempts to change registry settings need to be tracked, you can combine the Audit Registry policy setting with the Global Object Access Auditing policy settings to ensure that all attempts to modify registry settings on a computer are tracked.

• Object Access\Audit SAM. The Security Accounts Manager (SAM) is a database that is present on computers running Windows that stores user accounts and security descriptors for users on the local computer. Changes to user and group objects are tracked by the Account Management audit category. However, user accounts with the proper user rights could potentially alter the files where the account and password information is stored in the system, bypassing any Account Management events.

• Privilege Use\Audit Sensitive Privilege Use. Privilege Use policy settings and audit events allow you to track the use of certain rights on one or more systems. If you configure this policy setting, an audit event is generated when sensitive rights requests are made.

Network activity

The following network activity policy settings allow you to monitor security-related issues that are not necessarily covered in the data or user activity categories, but that can be equally important for network status and protection.

• Account Management [Auditing_Events]. The policy settings in this category can be used to track attempts to create, delete, or modify user or computer accounts, security groups, or distribution groups. Monitoring these activities complements the monitoring strategies you select in the user activity and data activity sections.

• Account Logon\Audit Kerberos Authentication Service and Account Logon\Audit Kerberos Service Ticket Operations. Audit policy settings in the Account Logon category monitor activities that relate to the use of domain account credentials. These policy settings complement the policy settings in the Logon/Logoff category. The Audit Kerberos Authentication Service policy setting allows you to monitor the status of and potential threats to the Kerberos service. The Audit Kerberos Service Ticket Operations policy setting allows you to monitor the use of Kerberos service tickets.

  Note

  Account Logon policy settings apply only to specific domain account activities, regardless of the computer that is accessed, whereas Logon/Logoff policy settings apply to the computer that hosts the resources being accessed.

• Account Logon\Audit Other Account Logon Events. This policy setting can be used to track a number of different network activities, including attempts to create Remote Desktop connections, wired network connections, and wireless connections.

• DS Access. Policy settings in this category allow you to monitor the AD DS role services, which provide account data, validate logons, maintain network access permissions, and provide other services that are critical to the secure and proper functioning of a network. Therefore, auditing the rights to access and modify the configuration of a domain controller can help an organization maintain a secure and reliable network. In addition, one of the key tasks performed by AD DS is the replication of data between domain controllers.

• Logon/Logoff\Audit IPsec Extended Mode, Logon/Logoff\Audit IPsec Main Mode, and Logon/Logoff\Audit IPsec Quick Mode. Many networks support large numbers of external users, including remote employees and partners. Because these users are outside the organization's network boundaries, IPsec is often used to help protect communications over the Internet by enabling network-level peer authentication, data origin authentication, data integrity, data confidentiality (encryption), and protection against replay attacks. You can use these settings to ensure that IPsec services are functioning properly.

• Logon/Logoff\Audit Network Policy Server. Organizations that use RADIUS (IAS) and Network Access Protection (NAP) to set and maintain security requirements for external users can use this policy setting to monitor the effectiveness of these policies and to determine whether anyone is attempting to circumvent these protections.

• Policy Change. These policy settings and events allow you to track changes to important security policies on a local computer or network. Because policies are typically established by administrators to help secure network resources, any changes or attempts to change these policies can be an important aspect of security management for a network.

• Policy Change\Audit Audit Policy Change. This policy setting allows you to monitor changes to the audit policy. If malicious users obtain domain administrator credentials, they can temporarily disable essential security audit policy settings so that their other activities on the network cannot be detected.

• Policy Change\Audit Filtering Platform Policy Change. This policy setting can be used to monitor a large variety of changes to an organization's IPsec policies.

• Policy Change\Audit MPSSVC Rule-Level Policy Change. This policy setting determines if the operating system generates audit events when changes are made to policy rules for the Microsoft Protection Service (MPSSVC.exe), which is used by Windows Firewall. Changes to firewall rules are important for understanding the security state of the computer and how well it is protected against network attacks.

Confirm operating system version compatibility

Not all versions of Windows support advanced audit policy settings or the use of Group Policy to apply and manage these settings. Refer to the supported versions of Windows designated in the Applies To list at the beginning of this topic for version-applicable information that relates to the information in this guide. For more information, see Which Editions of Windows Support Advanced Audit Policy Configuration.

The audit policy settings under Local Policies\Audit Policy overlap with audit policy settings under Security Settings\Advanced Audit Policy Configuration. However, the advanced audit policy categories and subcategories make it possible to focus your auditing efforts on the most critical activities while reducing the amount of audit data that is less important to your organization.

For example, Local Policies\Audit Policy contains a single setting called Audit account logon events. When this setting is configured, it generates at least 10 types of audit events.

In comparison, the Account Logon category under Security Settings\Advanced Audit Policy Configuration provides the following advanced settings, which allow you to focus your auditing:

• Credential Validation

• Kerberos Authentication Service

• Kerberos Service Ticket Operations

• Other Account Logon Events

These settings allow you to exercise much tighter control over which activities or events generate event data. Some activities and events will be more important to your organization, so define the scope of your security audit policy as narrowly as possible.

Success, failure, or both

Whichever event settings you include in your plan, you also have to decide whether you want to log an event when the activity fails, when an activity succeeds, or both successes and failures. This is an important question, and the answer will be based on the criticality of the event and the implications of the decision on event volume.

For example, on a file server that is accessed frequently by legitimate users, you may be interested in logging an event only when an unsuccessful attempt to access data takes place, because this could be evidence of an unauthorized or malicious user. And in this instance, logging successful attempts to access the server would quickly fill the event log with benign events.

On the other hand, if the file share has extremely sensitive and valuable information, such as trade secrets, you may want to log every access attempt, whether successful or unsuccessful, so that you have an audit trail of every user who accessed the resource.

Planning for security audit monitoring and management

Networks can contain hundreds of servers running critical services or storing critical data, all of which need to be monitored. The number of client computers on the network can easily range into the tens or even hundreds of thousands. This may not be an issue if the ratio of servers or client computers per administrator is low. Even if an administrator who is responsible for auditing security and performance issues has relatively few computers to monitor, you need to decide how an administrator will obtain event data to review. Following are some options for obtaining the event data.

• Will you keep event data on a local computer until an administrator logs on to review this data? If so, then the administrator needs to have physical or remote access to the Event Viewer on each client computer or server, and the remote access and firewall settings on each client computer or server need to be configured to enable this access. In addition, you need to decide how often an administrator can visit each computer, and adjust the size of the audit log so that critical information is not deleted if the log reaches its maximum capacity.

• Will you collect event data so that it can be reviewed from a central console? If so, there are a number of computer management products, such as the Audit Collection Services in Microsoft System Center Operations Manager 2007 and 2012, which can be used to collect and filter event data. Presumably this solution enables a single administrator to review larger amounts of data than using the local storage option. But in some cases, this can make it more difficult to detect clusters of related events that can occur on a single computer. For more information about ACS pertaining to these versions, see Audit Collection Services (ACS) or Collecting Security Events Using Audit Collection Services in Operations Manager.

In addition, whether you choose to leave audit data on an individual computer or consolidate it at a central location, you need to decide how large the log file should be and what should happen when the log reaches its maximum size. To configure these options, open Event Viewer, expand Windows Logs, right-click Security, and click Properties. You can configure the following properties:

• Overwrite events as needed (oldest events first). This is the default option, which is an acceptable solution in most situations.

• Archive the log when full, do not overwrite events. This option can be used when all log data needs to be saved, but it also suggests that you may not be reviewing audit data frequently enough.

• Do not overwrite events (Clear logs manually). This option stops the collection of audit data when the log file reaches its maximum size. Older data is retained at the expense of the most recent audit events. Use this option only if you do not want to lose any audit data, do not want to create an archive of the event log, and are committed to reviewing data before the maximum log size is reached.

You can also configure the audit log size and other key management options by using Group Policy settings. You can configure the event log settings in the following locations within the GPMC: Computer Configuration\Administrative Templates\Windows Components\Event Log Service\Security. These options include:

• Maximum Log Size (KB). This policy setting specifies the maximum size of the log files. The user interfaces in the Local Group Policy Editor and the Microsoft Management Console (MMC) Event Viewer snap-in allow you to enter values as large as 2 terabytes. If this setting is not configured, event logs have a default maximum size of 20 megabytes.

• Log Access. This policy setting determines which user accounts have access to log files and what usage rights are granted.

• Retain old events. This policy setting controls event log behavior when the log file reaches its maximum size. When this policy setting is enabled and a log file reaches its maximum size, new events are not written to the log and are lost. When this policy setting is disabled and a log file reaches its maximum size, new events overwrite old events.

• Backup log automatically when full. This policy setting controls event log behavior when the log file reaches its maximum size and takes effect only if the Retain old events policy setting is enabled. If you enable these policy settings, the event log file is automatically closed and renamed when it is full. A new file is then started. If you disable or do not configure this policy setting and the Retain old events policy setting is enabled, new events are discarded and the old events are retained.

For more information about the potential vulnerabilities addressed by these settings and their potential impacts, see the Threats and Countermeasures Guide: Security Settings in Windows Server 2008 and Windows Vista or the Threats and Countermeasures Guide: Security Settings in Windows Server 2008 R2 and Windows 7. Also, security policy settings are described in the Security Policy Settings Reference.

In addition, a growing number of organizations are being required to store archived log files for a number of years. You should consult with regulatory compliance officers in your organization to determine whether such guidelines apply to your organization. For more information, see the IT Compliance Management Guide.

Deploying the security audit policy

Before deploying the audit policy in a production environment, it is critical that you determine the effects of the policy settings that you have configured.

The first step in assessing your audit policy deployment is to create a test environment in a lab and use it to simulate the various use scenarios that you have identified to confirm that the audit settings you have selected are configured correctly and generate the type of results you intend. For more information about setting up a lab environment for testing security audit policy, see the Advanced Security Auditing Walkthrough.

However, unless you are able to run fairly realistic simulations of network usage patterns, a lab setup cannot provide you with accurate information about the volume of audit data that the audit policy settings you selected will generate and how effective your plan for monitoring audit data will be. To provide this type of information, you need to conduct one or more pilot deployments. These pilot deployments could involve:

• A single OU that contains critical data servers or an OU that contains all desktop computers in a specified location.

• A limited set of security audit policy settings, such as Logon/Logoff and Account Logon.

• A combination of limited OUs and audit policy settings—for example, targeting servers in only the Accounting OU with Object Access policy settings.

After you have successfully completed one or more limited deployments, you should confirm that the audit data that is collected is manageable with your management tools and administrators. When you have confirmed that the pilot deployment is effective, you need to confirm that you have the necessary tools and staff to expand the deployment to include additional OUs and sets of audit policy settings until the production deployment is complete.

For more information about modeling and deploying Group Policy, see the Group Policy Planning and Deployment Guide.