SQL Server Audit

Note: SQL Server Audit provides a robust mechanism for tracking database events. It's crucial for security compliance, forensic analysis, and understanding database activity.

SQL Server Audit allows you to monitor and audit database events for security-compliance and forensic analysis. You can define audit actions, specify where the audit data is stored (files, event logs, or the Windows Security log), and create audit policies to enforce auditing rules.

Key Concepts of SQL Server Audit

Server Audit: A server-level object that defines the destination for audit data and the data format.
Database Audit: A database-level object that defines which actions and objects to audit within a specific database.
Audit Action Groups: Collections of related SQL Server events that can be audited. For example, SUCCESSFUL_LOGIN_GROUP audits all successful logins.
Audit Specification: A server-level or database-level object that links one or more audit action groups to a server audit or database audit.

Steps to Implement SQL Server Audit

1. Create a Server Audit

First, you need to create a server audit that specifies the destination for your audit logs. You can use Transact-SQL (T-SQL) or SQL Server Management Studio (SSMS).

Using T-SQL:


CREATE SERVER AUDIT MyServerAudit
TO FILE (
    FILEPATH = 'C:\SQLAudits\'
    ,MAXSIZE = 50 MB
    ,MAX_ROLLOVER_FILES = 5
    ,RESERVE_DISK_SPACE = ON
)
WITH (
    QUEUE_DELAY = 1000
    ,ON_FAILURE = CONTINUE
);

Explanation:

FILEPATH: Specifies the directory where audit files will be stored.
MAXSIZE: Sets the maximum size of each audit file.
MAX_ROLLOVER_FILES: Determines the number of audit files to retain.
ON_FAILURE: Defines the server's behavior if writing to the audit destination fails. CONTINUE means the server will continue operating, potentially losing audit data. SHUTDOWN will stop the SQL Server instance.

2. Enable the Server Audit

After creating the audit, you need to enable it.


ALTER SERVER AUDIT MyServerAudit
TO FILE (FILEPATH = 'C:\SQLAudits\'); -- Re-specify destination if needed
GO

ENABLE SERVER AUDIT MyServerAudit;
GO

3. Create a Database Audit Specification

Next, create a database audit specification to define what to audit within a specific database and link it to the server audit.

Using T-SQL:


USE YourDatabaseName; -- Replace with your database name
GO

CREATE DATABASE AUDIT SPECIFICATION MyDatabaseAuditSpec
FOR SERVER AUDIT MyServerAudit
ADD (SCHEMA_OBJECT_CHANGE_GROUP)
ADD (SELECT_SERVER_STATE_GROUP)
ADD (UPDATE_SERVER_STATE_GROUP)
WITH (STATE = ON);
GO

Explanation:

ADD (SCHEMA_OBJECT_CHANGE_GROUP): Audits DDL statements like CREATE TABLE, ALTER TABLE, etc.
ADD (SELECT_SERVER_STATE_GROUP): Audits queries that select server state information.
ADD (UPDATE_SERVER_STATE_GROUP): Audits queries that update server state information.
WITH (STATE = ON): Enables the database audit specification immediately.

Viewing Audit Data

You can view audit data using T-SQL functions or SSMS.

Using T-SQL:

To read audit data from files:


SELECT *
FROM sys.fn_get_audit_file('C:\SQLAudits\*.sqlaudit', DEFAULT, DEFAULT);

To view audit specifications:


SELECT *
FROM sys.server_audits;

SELECT *
FROM sys.database_audit_specifications;

SELECT *
FROM sys.database_audit_specification_details;

Best Practices

Define Clear Auditing Requirements: Understand what needs to be audited for compliance and security.
Use Appropriate Audit Destinations: Choose file, Windows event log, or Security log based on your needs and infrastructure.
Configure Retention Policies: Ensure old audit data is managed appropriately to avoid filling up storage.
Regularly Review Audit Logs: Proactive monitoring can help detect suspicious activity early.
Limit Audited Events: Auditing too much can impact performance and generate excessive data. Focus on critical actions.

Tip: For sensitive data, consider auditing actions that read or modify that data, such as SELECT, INSERT, UPDATE, and DELETE operations.

Important: Ensure the SQL Server service account has read/write permissions to the directory specified in FILEPATH.

SQL Server Audit is a powerful tool that, when properly configured and monitored, significantly enhances the security posture of your database environment.

Last updated: 2023-10-27