Foreword
I'm a big fan of
Splunk
and similar tools for network and systems monitoring. This new generation of
machine data analysis brings a myriad of product and monitoring
opportunities. These systems work by indexing large swaths of machine
logging (logs, performance information, etc.) and providing an incredibly
effective interface for reporting of that information.To achieve this,
however, you need to provide very broad access to target systems.
If for any reason you can't use
Universal
Forwarders on Windows platforms, data collection can be
difficult. While Splunk provides
some
great documentation, it suffers from the same access (and
granting) problem as other platforms needing similar access. Generally this
problem is solved in one of two ways:
- Grant local administrator access on every machine to be monitored to a
single service account. Clearly this won't fly in organizations
concerned with granting the least amount of access needed for their
application portfolio. A single service account/group that has
administrator everywhere is a significant security risk.
- Use Group Policy to grant rights, ACLs,
etc. The problem with this approach is that some things cannot be
addressed by GPO
(WMI)
and if granting user rights often you cannot be granular enough
since each right defined must list all accounts/groups that get
that right. Across an enterprise that is a difficult and potentially
costly proposition. The main problem with setting user rights via Group
Policy is that the rights are not additive; they overwrite all entries
including required system or other application entries. This makes
central management of thousands of machines impractical. Say you need to
define "act as part of the operating system" for your monitoring
software; you would then need to centrally define every account/group
that has that right and any machine that needs to define that right in a
different way would need to obtain an override GPO for the machines in
question. While this is possible, many very large organizations find it
difficult to execute.
Neither one of these solutions is desirable in a medium to large sized
enterprise due to security requirements and management complexities. To
address this issue in a more granular way than the two options listed above,
we can use scripts to automate local configuration where necessary.
I'll be using Powershell scripts to perform the following tasks:
- Add Active Directory groups/users to local groups
- Grant WMI rights to Active Directory groups/users
- Grant local user rights to Active Directory groups/users
Assuming the affected security principals are not set elsewhere, we can set
these items with scripts that can be triggered via group policy. I'll be
using the GPO startup script functionality, but you can feel free to use any
other trigger mechanism you prefer (logon script, etc.). Note that this
solution
will work for products similar to Splunk that require
similar rights.
Execution
First things first, we need to establish what we'll be doing and principals
to which we want to grant access.
Assumptions
- Splunk indexer (or your other monitoring tool) installed and ready to
go
- You have administrative rights on all machines in question and Active
Directory rights sufficient to create the service account/group(s)
- You would rather use the Splunk Indexer to collect information rather
than install the Splunk
Universal Installer on your target machines (Good option as
well).
- Powershell 2.0 or newer & Windows 2003 or newer. This could be
done with batch/executables or VBScript but I won't be covering that.
Service Account/Group Setup
Per the
Splunk instructions, create a service account to run
Splunk. This will require administrative access on the machine running
Splunk, but nothing else (yet). It would be best to use a
managed service account but if you cannot a standard
account will be fine.
Splunk instructions deem that an Active Directory group need be created to
contain the service account. This isn't really necessary, but there are
potential advantages so we'll stick to it.
After creating/configuring that service account,
create the service account group and make your service
account a member. For the purposes of our demonstration I've named this
group "Splunk Accounts"
You should monitor this group to ensure no other accounts are added since
doing so would grant those accounts unwanted rights.
Now let's configure services. The service account
will need
to be local administrator on machines running the Splunk software (
splunkd,
splunkweb) directly
(more on this another time). After granting local admin, stop the Splunkd
and splunkweb services, change the logon to your new service account and
start them back up.
Now let's tackle the interesting part: granting granular rights to the
service account group.
Objective
Our objective is to grant the appropriate rights to the service account
group on every machine in our enterprise that we wish to monitor. Per the
documentation from Splunk, the minimum rights to collect Event Log and WMI
data remotely on a Windows platform are:
Misc
- WMI rights under root/cimv2
- DCOM launch permissions
User Rights
- Access this Computer from the Network
- Act as part of the operating system (I'd like to confirm this one;
not sure why)
- Log on as a batch job
- Log on as a service
- Profile System Performance
- Replace a process level token (not sure about this one either)
Local Group Membership
- Distributed COM Users
- Event Log Readers
- Performance Log Users
I'm sure you can see the why the official documentation prefers local
admin rights. :) Fortunately, we've got automation to do our heavy
lifting.
Scripts
Let's examine the scripts we'll be using. I've prepared four scripts for
this task:
- Powershell script to grant WMI and DCOM rights (Grant-WMIACL.ps1)
- Powershell script to grant User Rights (Grant-Rights.ps1)
- Powershell script to add local group membership and tie the others
together (Setup-Splunkuser.ps1)
- Batch file to launch powershell script correctly on all platforms
(SetupSplunkuser.bat)
Grant-WMIACL.ps1
As discussed, this script will grant the appropriate WMI and DCOM
access. This is based heavily on the work of
Steve Lee and
Karl Mitschke. Note that I've left options in the
script and commented out to change the level of access given to the WMI
objects, including the ability to toggle inheritance. I've left these in
to help you decipher the
SDDL structure. That said, the line that is not
commented out in this will work fine for our application. This script
could be run remotely (hence the $strComputer="localhost" line) but
we'll be using it locally (more on that below).
Grant-WMIACL.ps1 (Click to Expand) +
if ($args[0] -eq $null)
{
Write-Warning "No account or group name provided as an argument. Re-launch with the principal to grant rights to as the first argument."
Throw "I don't know what to do, please specify username, i.e. mydomain\myuser"
}
$Uname=$args[0]
Write-Warning "Granting WMI and DCOM access to $Uname..."
#This function gets a SID from an account name
function get-sid
{
Param ($DSIdentity)
$ID = new-object System.Security.Principal.NTAccount($DSIdentity)
return $ID.Translate( [System.Security.Principal.SecurityIdentifier] ).toString()
}
$sid = get-sid $Uname
#Enable Account, Remote Enable
#maps to "CC" SDDL_CREATE_CHILD ADS_RIGHT_DS_CREATE_CHILD , "WP" SDDL_WRITE_PROPERTY ADS_RIGHT_DS_WRITE_PROP
#$SDDL = "A;;CCWP;;;$sid"
#Provider Write(RP), Enable Account, Remote Enable
#maps to "RP" SDDL_READ_PROPERTY ADS_RIGHT_DS_READ_PROP , "CC" SDDL_CREATE_CHILD ADS_RIGHT_DS_CREATE_CHILD , "WP" SDDL_WRITE_PROPERTY ADS_RIGHT_DS_WRITE_PROP
#$SDDL = "A;;CCWPRP;;;$sid"
#Execute Methods(DC), Provider Write(RP), Enable Account, Remote Enable
#maps to "DC" SDDL_DELETE_CHILD ADS_RIGHT_DS_DELETE_CHILD , "RP" SDDL_READ_PROPERTY ADS_RIGHT_DS_READ_PROP , "CC" SDDL_CREATE_CHILD ADS_RIGHT_DS_CREATE_CHILD , "WP" SDDL_WRITE_PROPERTY ADS_RIGHT_DS_WRITE_PROP
#$SDDL = "A;;CCWPRPDC;;;$sid"
#Execute Methods(DC), Provider Write(RP), Enable Account, Remote Enable WITH INHERITENCE!! (note CI is in the header)
#maps to "CI" SDDL_CONTAINER_INHERIT CONTAINER_INHERIT_ACE , "DC" SDDL_DELETE_CHILD ADS_RIGHT_DS_DELETE_CHILD , "RP" SDDL_READ_PROPERTY ADS_RIGHT_DS_READ_PROP , "CC" SDDL_CREATE_CHILD ADS_RIGHT_DS_CREATE_CHILD , "WP" SDDL_WRITE_PROPERTY ADS_RIGHT_DS_WRITE_PROP
$SDDL = "A;CI;CCWPRPDC;;;$sid"
#Local Launch and Remote Activation
$DCOMSDDL = "A;;CCDCRP;;;$sid"
#Local Launch, Local Activation, Remote Launch, remote Activation
#$DCOMSDDL = “A;;CCDCLCSWRP;;;$sid”
#$computers = Get-Content "computers.txt"
#foreach ($strcomputer in $computers)
#{
$strComputer="localhost"
$Reg = [WMIClass]"\\$strComputer\root\default:StdRegProv"
$DCOM = $Reg.GetBinaryValue(2147483650,"software\microsoft\ole","MachineLaunchRestriction").uValue
$security = Get-WmiObject -ComputerName $strcomputer -Namespace root/cimv2 -Class __SystemSecurity
$converter = new-object system.management.ManagementClass Win32_SecurityDescriptorHelper
$binarySD = @($null)
$result = $security.PsBase.InvokeMethod("GetSD",$binarySD)
$outsddl = $converter.BinarySDToSDDL($binarySD[0])
$outDCOMSDDL = $converter.BinarySDToSDDL($DCOM)
$newSDDL = $outsddl.SDDL += "(" + $SDDL + ")"
$newDCOMSDDL = $outDCOMSDDL.SDDL += "(" + $DCOMSDDL + ")"
$WMIbinarySD = $converter.SDDLToBinarySD($newSDDL)
$WMIconvertedPermissions = ,$WMIbinarySD.BinarySD
$DCOMbinarySD = $converter.SDDLToBinarySD($newDCOMSDDL)
$DCOMconvertedPermissions = ,$DCOMbinarySD.BinarySD
#Set WMI Permissions
$result = $security.PsBase.InvokeMethod("SetSD",$WMIconvertedPermissions)
#Set DCOM Permissions
$result = $Reg.SetBinaryValue(2147483650,"software\microsoft\ole","MachineLaunchRestriction", $DCOMbinarySD.binarySD)
She's a beaut eh? Now for
Grant-Rights.ps1:
This one is huge because we're using full .NET code in the beginning. That
code is a combination of snippets from
here,
here, and
here. Note the comments displaying the short names
for some of the rights we can assign which I've left in to facilitate
applying this approach to systems other than Spunk. More can be found
here.
Grant-Rights.ps1 (Click to Expand) +
Add-Type @'
using System;
using System.Collections.Generic;
using System.Text;
namespace MyLsaWrapper
{
using System.Runtime.InteropServices;
using System.Security;
using System.Management;
using System.Runtime.CompilerServices;
using System.ComponentModel;
using LSA_HANDLE = IntPtr;
[StructLayout(LayoutKind.Sequential)]
struct LSA_OBJECT_ATTRIBUTES
{
internal int Length;
internal IntPtr RootDirectory;
internal IntPtr ObjectName;
internal int Attributes;
internal IntPtr SecurityDescriptor;
internal IntPtr SecurityQualityOfService;
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
struct LSA_UNICODE_STRING
{
internal ushort Length;
internal ushort MaximumLength;
[MarshalAs(UnmanagedType.LPWStr)]
internal string Buffer;
}
sealed class Win32Sec
{
[DllImport("advapi32", CharSet = CharSet.Unicode, SetLastError = true),
SuppressUnmanagedCodeSecurityAttribute]
internal static extern uint LsaOpenPolicy(
LSA_UNICODE_STRING[] SystemName,
ref LSA_OBJECT_ATTRIBUTES ObjectAttributes,
int AccessMask,
out IntPtr PolicyHandle
);
[DllImport("advapi32", CharSet = CharSet.Unicode, SetLastError = true),
SuppressUnmanagedCodeSecurityAttribute]
internal static extern uint LsaAddAccountRights(
LSA_HANDLE PolicyHandle,
IntPtr pSID,
LSA_UNICODE_STRING[] UserRights,
int CountOfRights
);
[DllImport("advapi32", CharSet = CharSet.Unicode, SetLastError = true),
SuppressUnmanagedCodeSecurityAttribute]
internal static extern int LsaLookupNames2(
LSA_HANDLE PolicyHandle,
uint Flags,
uint Count,
LSA_UNICODE_STRING[] Names,
ref IntPtr ReferencedDomains,
ref IntPtr Sids
);
[DllImport("advapi32")]
internal static extern int LsaNtStatusToWinError(int NTSTATUS);
[DllImport("advapi32")]
internal static extern int LsaClose(IntPtr PolicyHandle);
[DllImport("advapi32")]
internal static extern int LsaFreeMemory(IntPtr Buffer);
}
///
/// This class is used to grant "Log on as a service", "Log on as a batchjob", "Log on localy" etc.
/// to a user.
///
public sealed class LsaWrapper : IDisposable
{
[StructLayout(LayoutKind.Sequential)]
struct LSA_TRUST_INFORMATION
{
internal LSA_UNICODE_STRING Name;
internal IntPtr Sid;
}
[StructLayout(LayoutKind.Sequential)]
struct LSA_TRANSLATED_SID2
{
internal SidNameUse Use;
internal IntPtr Sid;
internal int DomainIndex;
uint Flags;
}
[StructLayout(LayoutKind.Sequential)]
struct LSA_REFERENCED_DOMAIN_LIST
{
internal uint Entries;
internal LSA_TRUST_INFORMATION Domains;
}
enum SidNameUse : int
{
User = 1,
Group = 2,
Domain = 3,
Alias = 4,
KnownGroup = 5,
DeletedAccount = 6,
Invalid = 7,
Unknown = 8,
Computer = 9
}
enum Access : int
{
POLICY_READ = 0x20006,
POLICY_ALL_ACCESS = 0x00F0FFF,
POLICY_EXECUTE = 0X20801,
POLICY_WRITE = 0X207F8
}
const uint STATUS_ACCESS_DENIED = 0xc0000022;
const uint STATUS_INSUFFICIENT_RESOURCES = 0xc000009a;
const uint STATUS_NO_MEMORY = 0xc0000017;
IntPtr lsaHandle;
public LsaWrapper()
: this(null)
{ }
// // local system if systemName is null
public LsaWrapper(string systemName)
{
LSA_OBJECT_ATTRIBUTES lsaAttr;
lsaAttr.RootDirectory = IntPtr.Zero;
lsaAttr.ObjectName = IntPtr.Zero;
lsaAttr.Attributes = 0;
lsaAttr.SecurityDescriptor = IntPtr.Zero;
lsaAttr.SecurityQualityOfService = IntPtr.Zero;
lsaAttr.Length = Marshal.SizeOf(typeof(LSA_OBJECT_ATTRIBUTES));
lsaHandle = IntPtr.Zero;
LSA_UNICODE_STRING[] system = null;
if (systemName != null)
{
system = new LSA_UNICODE_STRING[1];
system[0] = InitLsaString(systemName);
}
uint ret = Win32Sec.LsaOpenPolicy(system, ref lsaAttr,
(int)Access.POLICY_ALL_ACCESS, out lsaHandle);
if (ret == 0)
return;
if (ret == STATUS_ACCESS_DENIED)
{
throw new UnauthorizedAccessException();
}
if ((ret == STATUS_INSUFFICIENT_RESOURCES) || (ret == STATUS_NO_MEMORY))
{
throw new OutOfMemoryException();
}
throw new Win32Exception(Win32Sec.LsaNtStatusToWinError((int)ret));
}
public void AddPrivileges(string account, string privilege)
{
LSA_UNICODE_STRING[] names = new LSA_UNICODE_STRING[1];
LSA_TRANSLATED_SID2 lts;
IntPtr tsids = IntPtr.Zero;
IntPtr tdom = IntPtr.Zero;
names[0] = InitLsaString(account);
lts.Sid = IntPtr.Zero;
Console.WriteLine("String account: {0}", names[0].Length);
int ret1 = Win32Sec.LsaLookupNames2(lsaHandle, 0, 1, names, ref tdom, ref tsids);
if (ret1 != 0)
throw new Win32Exception(Win32Sec.LsaNtStatusToWinError(ret1));
lts = (LSA_TRANSLATED_SID2)Marshal.PtrToStructure(tsids, typeof(LSA_TRANSLATED_SID2));
IntPtr pSid = lts.Sid;
//IntPtr pSid = GetSIDInformation(account);
LSA_UNICODE_STRING[] privileges = new LSA_UNICODE_STRING[1];
privileges[0] = InitLsaString(privilege);
uint ret = Win32Sec.LsaAddAccountRights(lsaHandle, pSid, privileges, 1);
Win32Sec.LsaFreeMemory(tsids);
Win32Sec.LsaFreeMemory(tdom);
if (ret == 0)
return;
if (ret == STATUS_ACCESS_DENIED)
{
throw new UnauthorizedAccessException();
}
if ((ret == STATUS_INSUFFICIENT_RESOURCES) || (ret == STATUS_NO_MEMORY))
{
throw new OutOfMemoryException();
}
throw new Win32Exception(Win32Sec.LsaNtStatusToWinError((int)ret));
}
public void Dispose()
{
if (lsaHandle != IntPtr.Zero)
{
Win32Sec.LsaClose(lsaHandle);
lsaHandle = IntPtr.Zero;
}
GC.SuppressFinalize(this);
}
~LsaWrapper()
{
Dispose();
}
// helper functions
IntPtr GetSIDInformation(string account)
{
LSA_UNICODE_STRING[] names = new LSA_UNICODE_STRING[1];
LSA_TRANSLATED_SID2 lts;
IntPtr tsids = IntPtr.Zero;
IntPtr tdom = IntPtr.Zero;
names[0] = InitLsaString(account);
lts.Sid = IntPtr.Zero;
Console.WriteLine("String account: {0}", names[0].Length);
int ret = Win32Sec.LsaLookupNames2(lsaHandle, 0, 1, names, ref tdom, ref tsids);
if (ret != 0)
throw new Win32Exception(Win32Sec.LsaNtStatusToWinError(ret));
lts = (LSA_TRANSLATED_SID2)Marshal.PtrToStructure(tsids,
typeof(LSA_TRANSLATED_SID2));
Win32Sec.LsaFreeMemory(tsids);
Win32Sec.LsaFreeMemory(tdom);
return lts.Sid;
}
static LSA_UNICODE_STRING InitLsaString(string s)
{
// Unicode strings max. 32KB
if (s.Length > 0x7ffe)
throw new ArgumentException("String too long");
LSA_UNICODE_STRING lus = new LSA_UNICODE_STRING();
lus.Buffer = s;
lus.Length = (ushort)(s.Length * sizeof(char));
lus.MaximumLength = (ushort)(lus.Length + sizeof(char));
return lus;
}
}
public class LsaWrapperCaller
{
public static void AddPrivileges(string account, string privilege)
{
using (LsaWrapper lsaWrapper = new LsaWrapper())
{
lsaWrapper.AddPrivileges(account, privilege);
}
}
}
}
'@
#Access this Computer from the Network
#SeNetworkLogonRight
#
#Act as part of the operating system
#SeTcbPrivilege
#
#Log on as a batch job
#SeBatchLogonRight
#
#Log on as a service
#SeServiceLogonRight
#
#Profile System Performance
#SeSystemProfilePrivilege
#
#Replace a process level token
#SeAssignPrimaryTokenPrivilege
if ($args[0] -eq $null -or $args[1] -eq $null)
{
Write-Warning "Available privs:"
Write-Host ""
Write-Host "Access this Computer from the Network"
Write-Warning "SeNetworkLogonRight"
Write-Host ""
Write-Host "Act as part of the operating system"
Write-Warning "SeTcbPrivilege"
Write-Host ""
Write-Host "Log on as a batch job"
Write-Warning "SeBatchLogonRight"
Write-Host ""
Write-Host "Log on as a service"
Write-Warning "SeServiceLogonRight"
Write-Host ""
Write-Host "Profile System Performance"
Write-Warning "SeSystemProfilePrivilege"
Write-Host ""
Write-Host "Replace a process level token"
Write-Warning "SeAssignPrimaryTokenPrivilege"
Throw "I don't know what to do, please specify username,right, i.e. mydomain\myuser, SeServiceLogonRight"
}
$Uname=$args[0]
$Right=$args[1]
Write-Warning "Giving $Right to $Uname..."
[MyLsaWrapper.LsaWrapperCaller]::AddPrivileges($Uname, $Right)
Don't let the length of that code scare you off; the only part you need to
understand is the last few lines. Now let's examine
Setup-Splunkuser.ps1:
This script does a few things: defines the target for these privileges,
adds those to a series of groups, and ties the other scripts together. The
one thing you'll definitely want to modify is the entry at the top,
$SplunkAcct="MYDOMAIN\Splunk
Accounts". This should be the domain and group you created to host
the service account(s). The next line,
$localGroups="Distributed COM
Users","Event Log Readers","Performance Log Users" local groups
to which you want to add AD groups to, each in quotes and separated by
commas. What I've set it to here is perfect for Splunk, but feel free to
change it for your needs.
Setup-Splunkuser.ps1 (Click to Expand)
+
$SplunkAcct="MYDOMAIN\Splunk Accounts"
$localGroups="Distributed COM Users","Event Log Readers","Performance Log Users"
#Get-ScriptDirectory Function #
#############################################################
function Get-ScriptDirectory
{
$Invocation = (Get-Variable MyInvocation -Scope 1).Value
$path=Split-Path $Invocation.MyCommand.Path
# INSERT ESCAPE CHARACTERS FOR USING PATHS IN COMMANDS
$path=$path.replace('{','`{')
$path=$path.replace('}','`}')
$path=$path.replace('[','`[')
$path=$path.replace(']','`]')
$path
}
#**********************************************************************************************************************
#get directory
$ScriptDir=Get-ScriptDirectory
#grant rights
Invoke-Expression "$scriptdir\Grant-Rights.ps1 '$SplunkAcct' 'SeNetworkLogonRight'"
Invoke-Expression "$scriptdir\Grant-Rights.ps1 '$SplunkAcct' 'SeTcbPrivilege'"
Invoke-Expression "$scriptdir\Grant-Rights.ps1 '$SplunkAcct' 'SeBatchLogonRight'"
Invoke-Expression "$scriptdir\Grant-Rights.ps1 '$SplunkAcct' 'SeServiceLogonRight'"
Invoke-Expression "$scriptdir\Grant-Rights.ps1 '$SplunkAcct' 'SeSystemProfilePrivilege'"
Invoke-Expression "$scriptdir\Grant-Rights.ps1 '$SplunkAcct' 'SeAssignPrimaryTokenPrivilege'"
#grant WMI ACLs
Invoke-Expression "$scriptdir\Grant-WMIACL.ps1 '$SplunkAcct'"
#add local group access
#NOTE WE ARE CHANGING THE ACCT VARIABLE TO A FORWARDSLASH NOW DO ALL OTHER FUNCTIONS BEFORE THIS
$SplunkAcct=$SplunkAcct.replace('\','/')
foreach ($localGroup in $localGroups)
{
$lclGrp=[ADSI]"WinNT://$env:COMPUTERNAME/$localGroup,group"
$lclGrp.psbase.Invoke("Add",([ADSI]"WinNT://$SplunkAcct").path)
}
Now for the final piece to the puzzle:
SetupSplunkuser.bat:
This script exists to provide compatibility with 2008 (not R2) and lower.
Native Powershell scripts run correctly on 2008R2 and higher, but a batch
launched script will run from 2003 up with no problem. This will be the
script we'll use to kick everything off.
powershell.exe -nologo -noexit -file %~dp0\Setup-SplunkUser.ps1
Now that we have our scripts in place, we need to do the hard part. Run
them everywhere we would like in the enterprise.
Running the Scripts on Target Machines
As discussed earlier, there are several ways to accomplish this. The
solution I'll be using is Group Policy by utilizing the Startup
Script functionality in the Computer portion of the policy.
Setting up the group policy is easy, the difficult part is getting the
scripts to run correctly, but we'll worry about that when we get
there.
Determine Your Target Machines
If you want to configure Splunk access rights across all machines in
your domain you can plan on using the default domain policy GPO to roll
out these changes. If you're reading this article, however, I suspect
you want to be more targeted with your application of changes.
I recommend using
security filtering against the desired groups of
computers. If you don't already have groups you would like to use,
create a security group in Active Directory and add your desired
machines to it. To do this on a large scale, you can use something like
this.
After you have your target group(s) set up, you need to configure the
group policy you plan on using to execute the script. If this GPO
doesn't yet exist,
create it and apply the security filtering listed
above.
Edit the GPO using GPMC:
- After opening the GPO, navigate to "Computer Configuration->Policies->Windows
Settings->Scripts (Startup/Shutdown)
- Select "Startup".
- Click "Show Files..."; this will open a folder on your sysvol volume
associated with this Group Policy Object.
- After modifying accordingly (Setup-Splunkuser.ps1) copy all four
scripts into the folder. These will be automatically replicated to
all domain controllers in the domain.
- Back on the "Startup Properties" screen, ensure the "Scripts" tab
is selected (not Powershell Scripts) and click "Add".
- Type or browse to SetupSplunkUser.bat. And click "OK"
twice.
This now is triggered to run on reboot for all impacted machines, but
we're not done yet. We still have to navigate the oddly challenging
world of running Powershell scripts in the Windows environment.
Running Powershell Scripts in a Distributed Environment - The Problem
The hurdle using this solution is a larger problem: By default,
Powershell scripts are super scary and won't run in your environment for
two reasons:
- By default, running scripts requires those scripts be
signed.
- By default, scripts will not run from the "internet", and for some
reason the UNC path to the domain controller that may have just
authenticated you is considered the "internet" by Windows.
More
here. There are two ways to solve this
problem.
- Secure Way/PKI(Recommended): If you have an internal PKI you can sign all your scripts AND add
the signer cert(s) to the trusted publisher store on all targeted
machines in Active Directory.
- Not-So Secure Way/Disable Security: You can run scripts
from your DC by setting the execution policy in Powershell to
"Unrestricted" and adding your domain controller sysvol share to
the trusted sites zone in Internet Explorer configuration.
I will briefly discuss each solution.
Secure Solution - PKI
This is the preferred and most secure method. While you could do this
with certificates from a public authority, it is recommended that you
use your own
Active Directory integrated PKI for this. Here
is a very high-level overview of the steps:
- Acquire a code
signer cert from your PKI. If using a Windows PKI you can
use the "Code Signing" template, but it really should be
customized first. Export or save the public key (.cer) because
we'll need it later.
- Sign each script with the following code (substituting
scriptname.ps1 with the location of your script):
#This assumes you have only one code signing script
#use Get-Childitem cert:\CurrentUser\My -codesigning to see all and change index if necessary
$cert=@(Get-Childitem cert:\CurrentUser\My -codesigning)[0]
#Do this for each script and change scriptname.ps1 to the actual script name
Set-AuthenticodeSignature .\scriptname.ps1 $cert
- Copy the scripts into the sysvol share as outlined above.
- Edit the GPO you would like to use to distribute the script...
the same one you're using to run the scripts above would be the
perfect match.
- Navigate to "Computer Configuration->Policies->Windows
Settings->Security Settings->Public Key
Policies->Trusted Publishers"
- Right click->Import and select your public
key (.cer) corresponding to your code signing cert.
Close the GPO and you should now be good. Once the certificate
propagates to the target machines they'll run the signed scripts
without issue.
Alternative Solution A - Disable Security for this Script
- Edit the SetupSplunkUser.bat script and change
the line to:
powershell.exe -ExecutionPolicy Bypass -nologo -noexit -file %~dp0\Setup-SplunkUser.ps1
- Upload the file to your sysvol share as described above.
- If you have issues running the other Powershell scripts that
are called from the first, you may have to use some trickery:
such as this.
Alternative Solution B - Disable Security Permanently
- Edit the GPO you would like to use to distribute the script... the
same one you're using to run the scripts would be the perfect
match.
- Navigate to "Computer Configuration->Policies->Administrative
Templates->Windows Components->Windows
Powershell"
- Edit "Turn on Script Execution" and change it to "Enabled"
and "Allow all scripts". Click OK and close the GPO.
- Add your domain sysvol path (ensure you use your domain name, not
your domain controller name) to the trusted sites zone: see here and here. OR change the UACAsInternet property;
see here.
That should do it! Remote eventlog, WMI, and most other types of remote
collection should now work using Splunk.
Troubleshooting
If you have issues getting or determining if the scripts are running
successfully, try the following:
- Try executing SetupSplunkUser.bat from an elevated command prompt
on one of the target machines. Note any issues.
- To audit running in a test group, you can add a line like "ran
script Setup-SplunkUser.ps1" | Out-File "c:\temp\temp.txt" to
create a log of the script execution on each machine.
- Script execution should be logged in the Application Log of each
server.
With this information you should be able to better control the service
rights of Splunk or similar software in a large enterprise environment
and still keep your auditors happy. For an added bonus, you could use
Splunk itself for
security
auditing now that your're done.
