Auditing File Access on File Servers

This article was contributed by Liju Varghese, a Senior Premier Field Engineer from Canada, based on a recent engagement.

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Recently, I helped a customer achieve two objectives:

1. Audit access to sensitive content on the file servers and ensure the information is captured
2. Generate reports on a regular basis that would show WHO did WHAT to WHICH content and WHEN this was done.

I thought I would share this in case you found yourself wanting to do something similar.

A word of caution, though: Due to the wide scope of what can be audited and to the degree in which the information can be logged, it is very important that you first establish the audit objectives for your company as a whole and your department in particular. These objectives will also be influenced by the country you are in and any industry affiliation. Decisions will also have to be made regarding the retention policies of your audit logs.

Environment Overview

My lab setup consists of two domain controllers and a file server, all running Windows Server 2008 R2 and a Windows 7 workstation.

The Audit policy is configured within a Group Policy Object and linked to the Organizational Unit that contains the computer object of RootMS01.

The file server hosts the file shares, folders and files I will be setting up the Audit System Access Control List (SACL) on.

A few caveats:

1. Auditing has to be enabled in the system’s security policy and in the Access Control List of a resource to successfully log events
2. Audit policy can be enabled either through group policy or the local security policy
3. If this is a Windows Server 2008 R2 or later operating system I recommend using the Advanced Audit Policy Configuration (Computer Configuration\Windows Settings\Security Settings\Advanced Audit Policy Configuration\Audit Policies\) as opposed to the older Audit Policy (Computer Configuration\Windows Settings\Security Settings\Local Policies\Audit Policy\)
4. Do not mix use of both Advanced Audit Policy Configuration and the older Audit Policy: If you enable audit policy through Advanced Audit Policy Configuration either through group policy or the local security policy, I recommend using the Advanced Audit Policy Configuration at every level (local policy, site, domain and OU-linked group policy)

Enable Audit Policy

1. Create a Group Policy Object and name it something to the effect of File Server Audit Policy

2. Edit the GPO, browse to Computer Configuration\Windows Settings\Security Settings\Advanced Audit Policy Configuration\Audit Policies\ and define the following Audit Policy settings

The settings below are from the WS2008R2SP1 Member Server Security Compliance baseline of the Security Compliance Manager (SCM) – http://technet.microsoft.com/en-us/solutionaccelerators/cc835245.aspx with the exception of Object Access: File System which I enabled for Success

AUDIT POLICY	VALUE
Account Logon: Credential Validation	Success and Failure
Account Logon: Kerberos Authentication Service	No Auditing
Account Logon: Kerberos Service Ticket Operations	No Auditing
Account Logon: Other Account Logon Events	No Auditing
Account Management: Application Group Management	No Auditing
Account Management: Computer Account Management	Success
Account Management: Distribution Group Management	No Auditing
Account Management: Other Account Management Events	Success and Failure
Account Management: Security Group Management	Success and Failure
Account Management: User Account Management	Success and Failure
Detailed Tracking: DPAPI Activity	No Auditing
Detailed Tracking: Process Creation	Success
Detailed Tracking: Process Termination	No Auditing
Detailed Tracking: RPC Events	No Auditing
DS Access: Detailed Directory Service Replication	No Auditing
DS Access: Directory Service Access	No Auditing
DS Access: Directory Service Changes	No Auditing
DS Access: Directory Service Replication	No Auditing
Logon-Logoff: Account Lockout	No Auditing
Logon-Logoff: IPsec Extended Mode	No Auditing
Logon-Logoff: IPsec Main Mode	No Auditing
Logon-Logoff: IPsec Quick Mode	No Auditing
Logon-Logoff: Logoff	Success
Logon-Logoff: Logon	Success and Failure
Logon-Logoff: Network Policy Server	No Auditing
Logon-Logoff: Other Logon/Logoff Events	No Auditing
Logon-Logoff: Special Logon	Success
Object Access: Application Generated	No Auditing
Object Access: Certification Services	No Auditing
Object Access: Detailed File Share	No Auditing
Object Access: File Share	No Auditing
Object Access: File System	Success
Object Access: Filtering Platform Connection	No Auditing
Object Access: Filtering Platform Packet Drop	No Auditing
Object Access: Handle Manipulation	No Auditing
Object Access: Kernel Object	No Auditing
Object Access: Other Object Access Events	No Auditing
Object Access: Registry	No Auditing
Object Access: SAM	No Auditing
Policy Change: Audit Policy Change	Success and Failure
Policy Change: Authentication Policy Change	Success
Policy Change: Authorization Policy Change	No Auditing
Policy Change: Filtering Platform Policy Change	No Auditing
Policy Change: MPSSVC Rule-Level Policy Change	No Auditing
Policy Change: Other Policy Change Events	No Auditing
Privilege Use: Non Sensitive Privilege Use	No Auditing
Privilege Use: Other Privilege Use Events	No Auditing
Privilege Use: Sensitive Privilege Use	Success and Failure
System: IPsec Driver	Success and Failure
System: Other System Events	No Auditing
System: Security State Change	Success and Failure
System: Security System Extension	Success and Failure
System: System Integrity	Success and Failure

3. Also remember to set the following settings as well under Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options –

a. Audit: Force audit policy subcategory settings (Windows Vista or later) to override audit policy category settings to Enabled

b. Audit: Shut down system immediately if unable to log security audits to Disabled

Event Log Size

You may need to increase the size of the Security event log to accommodate the new events generated configure the following group policy settings. This can be done with the policy setting Computer Configuration\Administrative Templates\Windows Components\Event Log Service\Security – Maximum Log Size (KB). For maximum supported sizes see http://support.microsoft.com/kb/957662

Note: if you wish to archive old events, set Retain old events to Enabled and Backup log automatically when full to Enabled. By doing so, the event log file is automatically closed and renamed when it is full and a new file is then started. If you do not wish to retain old events, set Retain old events to Disabled.

Set up Audit System Access Control List (SACL)

The critical part is setting up the right amount of auditing for the right security principal and for the right resources. The image below shows the folder structure for which I will be setting up the audit entries:

I created an entry for UserHomeFolder that applies to the folder, subfolders and files, for the Builtin Administrators group for all accesses.

The rationale behind this is that since the users have exclusive rights to their home folders, besides them, only members of the local administrators group would have the ability to read or modify the contents of the folders.

Sample events

Here’s a selection of some of the types of events you can expect to see with auditing enabled:

Security Event Cleared

Log Name:      Security 
Source:        Microsoft-Windows-Eventlog 
Date:          8/14/2013 7:59:09 AM 
Event ID:      1102 
Task Category: Log clear 
Level:         Information 
Keywords:      Audit Success 
User:          N/A 
Computer:      RootMS01.Reskit.com 
Description: 
The audit log was cleared. 
Subject: 
        Security ID:   RESKIT\BWayne 
        Account Name:  BWayne 
        Domain Name:   RESKIT 
        Logon ID:      0x871de

Ownership of File Taken

Log Name:      Security 
Source:        Microsoft-Windows-Security-Auditing 
Date:          8/14/2013 1:39:46 AM 
Event ID:      4663 
Task Category: File System 
Level:         Information 
Keywords:      Audit Success 
User:          N/A 
Computer:      RootMS01.Reskit.com 
Description: 
An attempt was made to access an object. 
Subject: 
        Security ID:           RESKIT\pparker 
        Account Name:          pparker 
        Account Domain:               RESKIT 
        Logon ID:              0x1119f6 
Object: 
        Object Server: Security 
        Object Type:   File 
        Object Name:   C:\Shares\UserHomeFolder\BWayne\BusinessProposal.txt 
        Handle ID:     0x290 
Process Information: 
        Process ID:    0x7cc 
        Process Name:  C:\Windows\System32\dllhost.exe 
Access Request Information: 
        Accesses:      WRITE_OWNER 
        Access Mask:   0x80000

Security ACL on File Modified

Log Name:      Security 
Source:        Microsoft-Windows-Security-Auditing 
Date:          8/14/2013 1:41:39 AM 
Event ID:      4663 
Task Category: File System 
Level:         Information 
Keywords:      Audit Success 
User:          N/A 
Computer:      RootMS01.Reskit.com 
Description: 
An attempt was made to access an object. 
Subject: 
        Security ID:           RESKIT\pparker 
        Account Name:          pparker 
        Account Domain:               RESKIT 
        Logon ID:              0x1119f6 
Object: 
        Object Server: Security 
        Object Type:   File 
        Object Name:   C:\Shares\UserHomeFolder\BWayne\BusinessProposal.txt 
        Handle ID:     0x360 
Process Information: 
        Process ID:    0x730 
        Process Name:  C:\Windows\System32\dllhost.exe 
Access Request Information: 
        Accesses:      WRITE_DAC 
        Access Mask:   0x40000

Generic File Read

Log Name:      Security 
Source:        Microsoft-Windows-Security-Auditing 
Date:          8/14/2013 1:51:48 AM 
Event ID:      4663 
Task Category: File System 
Level:         Information 
Keywords:      Audit Success 
User:          N/A 
Computer:      RootMS01.Reskit.com 
Description: 
An attempt was made to access an object. 
Subject: 
        Security ID:           RESKIT\pparker 
        Account Name:          pparker 
        Account Domain:               RESKIT 
        Logon ID:              0x17235b 
Object: 
        Object Server: Security 
        Object Type:   File 
        Object Name:   C:\Shares\UserHomeFolder\BWayne\BusinessProposal.txt 
        Handle ID:     0x1b4 
Process Information: 
        Process ID:    0x2f8 
        Process Name:  C:\Windows\System32\dllhost.exe 
Access Request Information: 
        Accesses:      READ_CONTROL 
        Access Mask:   0x20000

Run scripts to report on 4663 events

The PowerShell script below queries the Security event log on one or more servers for events with id 4663. This event documents actual operations performed against files and other objects for which auditing is enabled in the Security tab. The script also lists the name of the object and the bitwise equivalent of the permissions were actually exercised.

Save the code below to a file with the .ps1 extension. On the first line, replace machine names with the names of your fileservers. And on the last line, replace the output file and folder name.

$server = "RootMS01","RootDC01" $out = New-Object System.Text.StringBuilder $out.AppendLine("ServerName,EventID,TimeCreated,UserName,File_or_Folder,AccessMask")$ns = @{e = "http://schemas.microsoft.com/win/2004/08/events/event"} foreach ($svr in $server)     {    $evts = Get-WinEvent -computer $svr -FilterHashtable @{logname="security";id="4663"} -oldest

    foreach($evt in $evts)         {         $xml = [xml]$evt.ToXml()

        $SubjectUserName = Select-Xml -Xml $xml -Namespace $ns -XPath "//e:Data[@Name=’SubjectUserName’]/text()" | Select-Object -ExpandProperty Node | Select-Object -ExpandProperty Value

        $ObjectName = Select-Xml -Xml $xml -Namespace $ns -XPath "//e:Data[@Name=’ObjectName’]/text()" | Select-Object -ExpandProperty Node | Select-Object -ExpandProperty Value

        $AccessMask = Select-Xml -Xml $xml -Namespace $ns -XPath "//e:Data[@Name=’AccessMask’]/text()" | Select-Object -ExpandProperty Node | Select-Object -ExpandProperty Value

        $out.AppendLine("$($svr),$($evt.id),$($evt.TimeCreated),$SubjectUserName,$ObjectName,$AccessMask")

        Write-Host $svr         Write-Host $evt.id,$evt.TimeCreated,$SubjectUserName,$ObjectName,$AccessMask

        }     } $out.ToString() | out-file -filepath C:\Temp\4663Events.csv

Here’s some typical output:

ServerName	EventID	TimeCreated	UserName	File_or_Folder	AccessMask
RootMS01	4663	08/14/2013 08:01:09	BWayne	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x20000
RootMS01	4663	08/14/2013 08:01:16	BWayne	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x80
RootMS01	4663	08/14/2013 08:01:16	BWayne	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x20000
RootMS01	4663	08/14/2013 08:01:19	BWayne	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x80
RootMS01	4663	08/14/2013 08:01:19	BWayne	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x20000
RootMS01	4663	08/16/2013 11:39:37	Administrator	C:\Shares\UserHomeFolder\BWayne	0x20000
RootMS01	4663	08/16/2013 11:39:55	Administrator	C:\Shares\UserHomeFolder\BWayne\New Text Document.txt	0x20000
RootMS01	4663	08/16/2013 11:40:05	Administrator	C:\Shares\UserHomeFolder\BWayne\New Text Document.txt	0x10000
RootMS01	4663	08/20/2013 10:58:34	Administrator	C:\Shares\UserHomeFolder\BWayne	0x20000
RootMS01	4663	08/20/2013 10:59:08	Administrator	C:\Shares\UserHomeFolder\LSkywalker	0x20000
RootMS01	4663	08/20/2013 10:59:23	Administrator	C:\Shares\UserHomeFolder\BWayne	0x20000
RootMS01	4663	08/20/2013 10:59:23	Administrator	C:\Shares\UserHomeFolder\BWayne	0x80
RootMS01	4663	08/20/2013 10:59:23	Administrator	C:\Shares\UserHomeFolder\BWayne	0x20000
RootMS01	4663	08/20/2013 10:59:23	Administrator	C:\Shares\UserHomeFolder\BWayne	0x1
RootMS01	4663	08/20/2013 10:59:23	Administrator	C:\Shares\UserHomeFolder\BWayne	0x40000
RootMS01	4663	08/20/2013 11:00:12	Administrator	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x20000
RootMS01	4663	08/20/2013 11:01:15	PParker	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x20000
RootMS01	4663	08/20/2013 11:01:15	PParker	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x1
RootMS01	4663	08/20/2013 11:02:19	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x80000
RootMS01	4663	08/20/2013 11:02:22	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:24	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:36	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:37	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:39	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:53	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:53	PParker	C:\Shares\UserHomeFolder\BWayne	0x20000
RootMS01	4663	08/20/2013 11:02:53	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x40000
RootMS01	4663	08/20/2013 11:02:53	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:56	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x20000
RootMS01	4663	08/20/2013 11:02:56	PParker	C:\Shares\UserHomeFolder\BWayne\HRStuff.txt	0x1
RootMS01	4663	08/20/2013 11:36:07	Administrator	C:\Shares\UserHomeFolder\LSkywalker\Projects.txt	0x20000
RootMS01	4663	08/20/2013 11:38:43	Administrator	C:\Shares\UserHomeFolder\LSkywalker	0x20000
RootDC01			Administrator	C:\Shares\UserHomeFolder\LSkywalker	0x20000

You can use the table below (taken from http://msdn.microsoft.com/en-us/library/windows/desktop/aa822867(v=vs.85).aspx ) to interpret the AccessMask values to the file and directory access rights.

AccessMask Value	Constant	Description
0 (0x0)	FILE_READ_DATA	Grants the right to read data from the file.
0 (0x0)	FILE_LIST_DIRECTORY	Grants the right to read data from the file. For a directory, this value grants the right to list the contents of the directory.
1 (0x1)	FILE_WRITE_DATA	Grants the right to write data to the file.
1 (0x1)	FILE_ADD_FILE	Grants the right to write data to the file. For a directory, this value grants the right to create a file in the directory.
4 (0x4)	FILE_APPEND_DATA	Grants the right to append data to the file. For a directory, this value grants the right to create a subdirectory.
4 (0x4)	FILE_ADD_SUBDIRECTORY	Grants the right to append data to the file. For a directory, this value grants the right to create a subdirectory.
8 (0x8)	FILE_READ_EA	Grants the right to read extended attributes.
16 (0x10)	FILE_WRITE_EA	Grants the right to write extended attributes.
32 (0x20)	FILE_EXECUTE	Grants the right to execute a file.
32 (0x20)	FILE_TRAVERSE	Grants the right to execute a file. For a directory, the directory can be traversed.
64 (0x40)	FILE_DELETE_CHILD	Grants the right to delete a directory and all the files it contains (its children), even if the files are read-only.
128 (0x80)	FILE_READ_ATTRIBUTES	Grants the right to read file attributes.
256 (0x100)	FILE_WRITE_ATTRIBUTES	Grants the right to change file attributes.
65536 (0x10000)	DELETE	Grants the right to delete the object.
131072 (0x20000)	READ_CONTROL	Grants the right to read the information in the security descriptor for the object.
262144 (0x40000)	WRITE_DAC	Grants the right to modify the DACL in the object security descriptor for the object.
524288 (0x80000)	WRITE_OWNER	Grants the right to change the owner in the security descriptor for the object.
1048576 (0x100000)	SYNCHRONIZE	Grants the right to use the object for synchronization.

Remember to also report on the following events:

1. 4670 (Authorization Policy Change)
2. 4907 (Audit Policy Change), and
3. 1102 (Log clear)

Setting up Custom Views in Event Viewer

You can create a filter that includes events from multiple event logs that satisfy specified criteria. You can then name and save that filter as a custom view. To apply the filter associated with a saved custom view, you navigate to the custom view in the console tree and click its name. See http://technet.microsoft.com/en-us/library/cc709635.aspx for steps on how to create a Custom View.

As an example, the following filter looks for file access events by a user with sAMAccountName pparker:

<QueryList> 
  <Query Id="0" Path="Security"> 
    <Select Path="Security"> 
     *[System[(EventID=4663)]] 
     and 
     *[EventData[Data[@Name=’SubjectUserName’] and (Data=’pparker’)]]  
    </Select> 
  </Query> 
</QueryList>

Final Thoughts

1. If you need to set up audit SACLs on a large number of files, Global Object Access Auditing lets you create System Access Control Lists (SACL) for the entire computer, based on file and registry. See http://blogs.technet.com/b/askds/archive/2011/03/10/global-object-access-auditing-is-magic.aspx for more information

2. Enabling Object Access: File Share audit policy will generate very helpful 5145 events like the one below:

Log Name:      Security 
Source:        Microsoft-Windows-Security-Auditing 
Date:          8/14/2013 2:08:25 AM 
Event ID:      5145 
Task Category: Detailed File Share 
Level:         Information 
Keywords:      Audit Success 
User:          N/A 
Computer:      RootMS01.Reskit.com 
Description: 
A network share object was checked to see whether client can be granted desired access. 
Subject: 
        Security ID:           RESKIT\Administrator 
        Account Name:          Administrator 
        Account Domain:               RESKIT 
        Logon ID:              0x49199 
Network Information:    
        Object Type:           File 
        Source Address:               10.10.10.11 
        Source Port:           61361 
Share Information: 
        Share Name:            \\*\Shares 
        Share Path:            \??\C:\Shares 
        Relative Target Name:  UserHomeFolder\LSkywalker\Projects.txt 
Access Request Information: 
        Access Mask:           0x120089 
        Accesses:              READ_CONTROL 
                              SYNCHRONIZE 
                              ReadData (or ListDirectory) 
                              ReadEA 
                              ReadAttributes 
Access Check Results: 
        READ_CONTROL:  Granted by Ownership 
                              SYNCHRONIZE:   Granted by        D:(A;;FA;;;WD) 
                              ReadData (or ListDirectory):  Granted by        D:(A;;FA;;;WD) 
                              ReadEA: Granted by     D:(A;;FA;;;WD)

However, since there are no SACLs for shares, once this setting is enabled, access to all shares on the system will be audited and a large volume of these events will be generated.

3. A backup job running under the context of a local administrator on the file server will also generate a large volume of 4663 events. The command AuditPol /Set /User:Reskit\BackupAcct /Subcategory:”File System” /Success:Enable /Exclude can be used for a user-level exclusion. However this setting is not honored for users who are members of the Administrators local group.