How to Audit Login Changes on a SQL Server

For instance, if you want to detect what logins have been created, deleted, or modified since the last audit, a purely T-SQL solution can be implemented quickly and easily. We'll tackle something that provides slightly more information in this tip.

First, the basic tables we'll need to do the auditing. We'll need a table to store the current scan information as well as a table to store our scan history. We'll actually compare the two tables in order to determine what has changed between audits.  We'll also need a table to track when we did our scans.

Here are the three tables:

CREATE TABLE dbo.AuditScan (

 AuditScanID INT IDENTITY(1,1) NOT NULL,

 ScanStartDate datetime NOT NULL,

 ScanEndDate datetime NULL,

 CONSTRAINT PK_AuditScan PRIMARY KEY CLUSTERED (AuditScanID)

);

GO 

CREATE TABLE dbo.CurrentLoginScan (

 [sid] VARBINARY(85) NOT NULL,

 [name] sysname NOT NULL,

 [type] CHAR(1) NOT NULL,

 create_date DATETIME,

 modify_date DATETIME,

 AuditScanID INT NOT NULL,

 CONSTRAINT PK_CurrentLoginScan PRIMARY KEY CLUSTERED ([sid]),

 CONSTRAINT FK_CurrentLoginScan_AuditScan FOREIGN KEY (AuditScanID) 

 REFERENCES dbo.AuditScan (AuditScanID)

);

GO 

CREATE TABLE dbo.LoginScanRecord (

 [ScanLogID] INT NOT NULL IDENTITY(1,1),

 [AuditScanID] INT NOT NULL,

 [sid] VARBINARY(85) NOT NULL,

 [name] sysname NOT NULL,

 [type] CHAR(1) NOT NULL,

 create_date DATETIME NOT NULL,

 modify_date DATETIME NOT NULL,

 CONSTRAINT PK_LoginSCanRecord PRIMARY KEY CLUSTERED (ScanLogID),

 CONSTRAINT FK_LoginScanRecord_AuditScan FOREIGN KEY (AuditScanID) 

 REFERENCES dbo.AuditScan (AuditScanID)

);

GO 

Now we'll need a couple of stored procedures to mark the start and stop of each audit.

CREATE PROC dbo.StartAuditScan 

  @AuditScanID INT OUTPUT

AS

BEGIN

  SET NOCOUNT ON;

  DECLARE @AuditScanIDTable TABLE(AuditScanID INT);

  INSERT INTO dbo.AuditScan (ScanStartDate) 

    OUTPUT INSERTED.AuditScanID INTO @AuditScanIDTable

  VALUES (GETDATE());

  SET @AuditScanID = (SELECT AuditScanID FROM @AuditScanIDTable);

END;

GO 

CREATE PROC dbo.EndAuditScan

  @AuditScanID INT

AS

BEGIN

  SET NOCOUNT ON;

  UPDATE dbo.AuditScan

  SET ScanEndDate = GETDATE()

  WHERE AuditScanID = @AuditScanID;

END;

GO 

And finally, we'll need the stored procedure that does the audit itself. It's going to do the following:

1. Start the audit.
2. Retrieve the pertinent information from the sys.server_principals view into the CurrentLoginScan table.
3. Compare to see what new logins have been created since the last audit.
4. Compare to see what logins have been deleted since the last audit.
5. Compare to see what logins show a change since the last audit.
6. End the audit.
7. Report the findings.

Here's the stored procedure that accomplishes the above.

CREATE PROC dbo.ExecuteLoginScan

AS

BEGIN

  SET NOCOUNT ON;

  DECLARE @CurrentScanID INT;

  DECLARE @PreviousScanID INT;

  SET @PreviousScanID = (SELECT MAX(AuditScanID) FROM dbo.AuditScan);

  EXEC dbo.StartAuditScan @CurrentScanID OUTPUT;

  EXEC dbo.EndAuditScan @CurrentScanID;

  INSERT INTO dbo.CurrentLoginScan

  ([sid], [name], [type], create_date, modify_date, AuditScanID)

  SELECT [sid], [name], [type], create_date, modify_date, @CurrentScanID

  FROM master.sys.server_principals;

  CREATE TABLE #LoginScanReport (

    Change VARCHAR(20) NOT NULL,

    [sid] VARBINARY(85) NOT NULL,

    [Current_Name] sysname NULL,

    [Old_Name] sysname NULL,

    [Current_Type] CHAR(1) NULL,

    [Old_Type] CHAR(1) NULL,

    [Current_Create_Date] DATETIME NULL,

    [Old_Create_Date] DATETIME NULL,

    [Current_Modify_Date] DATETIME NULL,

    [Old_Modify_Date] DATETIME NULL

  );

  -- Find new logins

  INSERT INTO #LoginScanReport 

  (Change, [sid], Current_Name, Current_Type, Current_Create_Date, Current_Modify_Date)

  SELECT 'Added', Curr.[sid], Curr.[name], Curr.[type], Curr.create_date, Curr.modify_date

  FROM dbo.CurrentLoginScan Curr

    LEFT JOIN (SELECT [sid], [name], [type], create_date, modify_date 

               FROM dbo.LoginScanRecord 

               WHERE AuditScanID = @PreviousScanID) Old

      ON Curr.[sid] = Old.[sid]

  WHERE Old.[sid] IS NULL;

  -- Find deleted logins

  INSERT INTO #LoginScanReport 

  (Change, [sid], Old_Name, Old_Type, Old_Create_Date, Old_Modify_Date)

  SELECT 'Deleted', Old.[sid], Old.[name], Old.[type], Old.create_date, Old.modify_date

  FROM dbo.CurrentLoginScan Curr

    RIGHT JOIN (SELECT [sid], [name], [type], create_date, modify_date 

               FROM dbo.LoginScanRecord 

               WHERE AuditScanID = @PreviousScanID) Old

      ON Curr.[sid] = Old.[sid]

  WHERE Curr.[sid] IS NULL;

  -- Find Changed Logins

  INSERT INTO #LoginScanReport 

  (Change, [sid], Current_Name, Current_Type, Current_Create_Date, Current_Modify_Date,

                  Old_Name, Old_Type, Old_Create_Date, Old_Modify_Date)

  SELECT 'Modified', Curr.[sid], Curr.[name], Curr.[type], Curr.create_date, Curr.modify_date,

                     Old.[name], Old.[type], Old.create_date, Old.modify_date

  FROM dbo.CurrentLoginScan Curr

    JOIN (SELECT [sid], [name], [type], create_date, modify_date 

          FROM dbo.LoginScanRecord 

          WHERE AuditScanID = @PreviousScanID) Old

      ON Curr.[sid] = Old.[sid]

  WHERE (Curr.[name] <> Old.[name]) OR (Curr.[type] <> Old.[type]) 

         OR (Curr.create_date <> Old.create_date) OR (Curr.modify_date <> Old.modify_date);

  INSERT INTO dbo.LoginScanRecord

  (AuditScanID, [sid], [name], [type], create_date, modify_date)

  SELECT AuditScanID, [sid], [name], [type], create_date, modify_date

  FROM dbo.CurrentLoginScan;

  DELETE FROM dbo.CurrentLoginScan;

  SELECT Change, [sid], Current_Name, Old_Name, Current_Type, Old_Type, 

    Current_Create_Date, Old_Create_Date, Current_Modify_Date, Old_Modify_Date

  FROM #LoginScanReport;  

END;

GO