Category: Windows

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Validating Windows Creds

I wanna make a really quick post here about this. Normally I generally right click a app on the taskbar, and then shift+right click the app icon, and in the context menu pick “run as a different user”. then I get a credentials box prompt asking me to enter the creds of the user and their password, and if successful open the app (generally cmd).

This time I was testing some old credentials used for a particular service, but I wasn’t sure of the password, I also wasn’t sure exactly where this account was all used, so was hesitant to just go and change the accounts password.

I did my usual trick as stated above and got the user was not allowed local logon for this machine, which was a good thing, some standard best practices for the account were implemented. This however still left me with the assumption the user/password was correct, but not 100% sure.

attempting the same thing with a random known bad password sure enough responded with wrong username/password. Giving me pretty confident results the username and password I entered were correct.

I found this serverfault post about the same question, and I attempted the simple “net use” trick. Sure enough they also do the run as trick I stated in the first paragraph.

net use \\%userdnsdomain% /user:%userdomain%\%username% *

on my main machine I got an error of multiple connections not allowed, I attempted the fix posted by themadmax

net use /delete \\unc\path

which didn’t work probably cause this path I was testing against was a mapped drive for my local logged in user. I followed up by running the commands from an alternative machine I knew had access to the share and DC’s.

Sure enough this worked, I am now confident the username and password are correct.

Hope this helps someone!

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Auto Install Defender Updates, but Not All Updates

Issue

Fun times! Updates. Which are not separated in the defined GPOs available to Sys Admins.

Many sources of this issue:
[SOLVED] Server 2016 – Auto install definition updates but nothing else? – Windows Server – Spiceworks

Autoupdate Windows Defender (microsoft.com)

Windows Server 2016 auto install security updates – Microsoft Q&A

Issue: Defender Definition updates come ever day, no separate GPO to differentiate other Windows system updates from these. Other updates require manual install for service availability reasons.

*NOTE* This is how to do this while retaining the update option #3: Auto Download and notify for install. Incase you need to maintain guided (human controlled) updates, but not for the definition updates.

Solution:

Use either:

For 2008 R2 (Source)
A) C:\Program Files\Windows Defender\MpCmdRun.exe -Signature Update

For 2016 + 2019 (Source)
B) PowerShell Cmdlet: Update-MpSignature

Implementation:

Create a script, configure a GPO to deploy it to server as a scheduled task.
*This post to be update with better, step by step tasks. Just a place holder for now with references.

Step 1: Create a script

If you need help with this, you can use my script as a reference, or just use it, similar to this.

Step 2: Determine shared location

Save the script to a share available to domain system (I heard SYSVOL is accessible by all). If this is not acceptable you can follow this guys guide in which he creates a standard SMB share from an alternative server.

Step 3: Fall Down a Rabbit Hole

OK… this is where things got a bit tricky. There’s one slight issue if you want to run a task from a systems’ perspective when the source is on a SMB share that requires domain creds. In the guide I provided about the Op simply created a shortcut link to the network shared script, which will run under a users context.

In this guide, by SysOps, he mentions the use of SYSTEM and the escalated privilege’s it has, but later mentions that he’s sourcing the script local but you could use a network share, however, not mentioning the issue I just did here.

Of course I figured, ok what a good time learn using gMSA accounts to run the task. It should be able to read the script file, it should have the required rights. (expect this is super good to know Thanks Leon! – If you have “Run whether user is logged in or not” your gMSA must be member of the Log on as a batch job or the local Administrators group to be able to run.) Also don’t have to worry about managing a password for the account, it should be a win all around. Let’s do it.

Pick Your Poison

You can either A) copy the script to a local path on the server, and create a scheduled task to run the script, either as system, or any standard user.

or B) create a domain account, or gMSA, and place the script in a SMB location and use a GPO to create the scheduled task on all machines.

I choose B…. but….

This is a bit of a rabbit hole so feel free to avoid this tangent by skipping to part B.

Turns out there’s no governance around the ExecutionPolicy in windows.

Microsoft has changed how definition updates are seen in update history.

Note usually you should grant access to manage the machine password permission to a group, instead of machines directly, and if done so permission to the gMSA can be applied without reboot. (Though I’m sure the same might apply when applied directly to the system as well, but I have tested).

Now my mind started to wonder a bit, Is there a limitation to how many machines can have access to a gMSA? Even this more nitty gritty blog post on gMSAs doesn’t seem to state any limitations. This reddit post asking specifically around gMSA limitation.. nothing.

“unique_username065
3 years ago
You also need to give the gMSA permission to run scripts. There is a technet blog article that explains all the necessary steps to run scheduled tasks and scripts. I am on mobile, so I can’t look for it.

Just be very careful because everyone with access to the machine can potentially exploit gMSAs AFAIK.

Disclaimer: all I wrote is based in theories”

Well that TechNet blog would have been useful, I’ll keep sourcing my findings as we move along here.  So I’ll test it on a single machine, but I have multiple systems in an OU which ties GPOs, so how to push a GPO to just one machine in a OU?

Of course this has it’s own rabbit hole you have to consider… See here for all the details.

In short… ‘If adding “Authenticated Users” with just “Read” permissions is not an option in your environment, then you will need to add the “Domain Computers” group with “Read” Permissions. If you want to limit it beyond the Domain Computers group: Administrators can also create a new domain group and add the computer accounts to the group so you can limit the “Read Access” on a Group Policy Object (GPO).’

In my case the computer account it’s self should suffice, or as mentioned a group with computer accounts. This was the scope and the read permission will both be applied via the same group, and if needing to add more machine only need to add them to the appropriate groups not mess with GPO scopes or permissions. (AKA scalable design)

Then I had one final question pop in my head, “If you can define a GPO to copy a file from a shared network path to the local machine, how does it do that? If scheduled Tasks can only run via ‘SYSTEM’.”

My highly intelligent friend said something, and seems to be backed by this source as well.

“This can only be done during system startup – you’re copying to a system protected folder. During system startup you’ll need to grant the computer itself read access to the source directory share. There are two ways of doing this.

– Create a computer group and grant that group read access. You’ll then need to add every computer to it. You could use the built in Domain Computers group for this as well

or

– Put all the files you want copied into the GPO folder. This folder is read-only for computers as they start.”

Ohhh weird… but you can’t use the computer account to run scheduled tasks?

Apparently not well poop. So that explains all that….

I wanted to test my script as a scheduled task, and noticed a random change from the last time I test.

Old results: Click Check for updates, Definition Update was available, but had to click Install for them to be installed.,

New results (without deploying this script): Click check for update, definition update installs by itself after clicking check for update.

Oh well in that case, lets just up the amount of times it checks for updates.

Apply the GPO setting “Automatic Updates Detection Frequency”

Check the next morning….

As you can see, the detection frequency was applied, but I guess it’s not being adhered to. The last update is well beyond 2 hours.

Time to deploy the script.

K so to pull this off…

Step 3: Create a gMSA

  1. create a group for granting access to manage the MSA password 
    New-ADGroup -Name "Update Defender Definitions" -SamAccountName UpdateDefenderDefinitions -GroupCategory Security -GroupScope DomainLocal -DisplayName "Update Defender Definitions" -Description "This group is granted ManagePassword rights on the gMSAtskUDDspt" -Path "CN=Managed Service Accounts,DC=zewwy,DC=ca"
  2. create the gmsa 
    New-ADServiceAccount -Name gMSAtskUDDspt -DNSHostName gMSAtskUDDspt.zewwy.ca -PrincipalsAllowedToRetrieveManagedPassword UpdateDefenderDefinitions
  3. grant the group access to the GMSA, by adding computers into the group created in step 1. 
    Add-ADGroupMember -Identity SvcAccPSOGroup -Members SQL01,SQL02

    Step 4: Create a GPO that creates a Scheduled Task to run the script

Right click in GPMC where you want your GPO to be linked, and select “create new GPO and link it here”

Remove Authenticated Users from the scope (if you need to test this one one machine, when multiple machines are in one OU, else skip this stuff). Then add the computer account in the scope area. (It appears the computer account is granted read rights on the GPO now.)

Edit the GPO -> Computer -> Preferences -> Scheduled Tasks (at least Windows 7)

It’s super important to know the differences between the actions types.

Action : Update Create

Name: InstallDefinitionUpdates

[Document remaining steps]

Caveats

Shit… I forgot, you have to add the gMSA to all computers that would need this applied too.. and you can’t automate that via GPO, like you can everything else.

Did a update force and saw the scheduled task, finally something, but…

I clearly forgot about Leon’s advise… and double checking that the option to run if the user is logged in or not.

gpupdate /force….. no change to task…. what… ok delete task…..

gpupdate /force… No new task… what?

Go to GPO, switch the option back to run when user is logged on…

gpupdate /force… new task is there… OK what gives?

Try to set the task to run if user is logged on or not manually by editing the task…. I get a cred box pop-up. As for most services using gMSAs, left the password field blank and clicked ok…

I love IT work….

OK… what did I miss this time?

OK, I’ve been digging in the PowerShell properties for scheduled tasks for a while now… How the heck do I set to run logged on or not via powershell?

Main answer, says to use a principal with type password, but it’s a service account? Second main answer says to use system, like no this is a gMSA and we need a domain account for the issues stated above. For shits I tried setting the principal logon type to S4U, as mentioned by one commenter, but it gave me access denied response, then I picked password type and it took it, somehow it is set now… what?! (See picture below)

I went to check the task history… It worked!

Holy Bloody Mary, it actually worked!

OK but it’s seem really stupid when you define the option to run when logged on or not it won’t deploy the task, but if you leave it as user as to logon it does, then you have to use powershell to set the proper logontype. So another powershell script… Ughhhh, there’s also the issue of installing the gMSA on the computer account, I wonder if I could have two additional tasks to run powershell commands to those needfuls.

Ahhh crap, if the GPO action is replace… and I just had to do manual steps I haven’t automated yet….

gpupdate /force… yup back to run when user is logged on crap! Normally the replace action is good if you want to make changes, in this case it’s not wanted, and would be kind of redic to have these multiple scripts to fix themselves go off every time there’s a gpupdate. In this case I changed the Action back to create. K that works, but how do I run these simple powershell commands right after that… automatically.

$principal = New-ScheduledTaskPrincipal -UserId domain\gMSA$ -LogonType password
Set-ScheduledTask -TaskName InstallDefinitionUpdates -Principal $principal

For the first issue, this was the closest I could find. The main answer of using LAPS is poop. The issue around credSSP could be the fact, but not sure if putting creds into a script is a great idea anyway if it is required. I wonder if the system account can run the command… or the “Computer account” maybe via a simplified startup script?

Sine the amount of systems I had to deploy on was small, I skipped this. But if this was wanting to be deployed on end machines, workstations, or laptops. This might be a required step in that case.

As for Issue number two. I ran the above commands manually after installing the gMSA manually. At this point it makes you wonder what was the point of automating the creation of the scheduled task, if I simply have to manually do the other steps. The only answer to that I have is, I didn’t know, I learnt as I go. However it only now required 2 more hurdles to resolve to actually fully automate the process.

Summary

This was another very painful learning experience, all cause definition updates were tied to MS updates, and couldn’t have their own install schedule or install action. I going to create a separate blog post to cover creating a Scheduled Task with a gMSA like this one did. but more specific to that task.

May I suggest you use a standard domain account and just deploy a script pointing to that, and store the creds somewhere if you really need to. This is a painful process.

 

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Get Windows Server out of Stuck Update State

I probably should be a bit more clear, this post will cover how I managed to get a Windows Server 2016 to “check for updates” when it had gone wrong and was stuck looping (checking) and failing where it replaces the “check for updates” button with nothing other than “retry”.

This happened after clicking “Search Microsoft Online for Updates” in which case it found a couple that were not approved by WSUS or not selected as category’s that WSUS actually downloads.

Funny in this case after I did what will be mentioned below, clicking retry did just start checking again, and then stated “Your device is up to date”.

So ok it worked that time, but what I discovered at the time, was that there’s a new command to use on the backend (command line) to do the needful when the UI doesn’t have the appropriate button available. Like usual Microsoft fashion, notifying stakeholders was poor, and so was an documentation.

Now this isn’t the first time I discussed issues around Windows update, in particular around the tool MS has given Syadmins to do the needful; WSUS. Such as this time, when clients are not showing up within WSUS after clearly showing they had applied the GPOs (registries) required and no network issues between them, or this time CU updates weren’t being downloaded by WSUS although clearly the types and categories were fully correct.

In this case however instead the issue was simply what commands to use, as stated within the original person asking the question in the TechNet link above “Since wuauclt has been depreciated in windows 10, I was googling what has replaced it.

I found that usoclient is what has replaced this command for windows update in the command line. ”

What authoritative source is there for this claim, well I found this…

“The wuauclt.exe /detectnow command has been removed and is no longer supported. To trigger a scan for updates, do either of the following:

  • Run these PowerShell commands: 
    $AutoUpdates = New-Object -ComObject "Microsoft.Update.AutoUpdate"
$AutoUpdates.DetectNow()
  • Alternately, use this VBScript: 
    Set automaticUpdates = CreateObject("Microsoft.Update.AutoUpdate")
automaticUpdates.DetectNow()

”

Funny thing about this is I found that wuauclt /reportnow still works in Server 2016, as noted in my other blog posts. I generally didn’t use /detectnow. However what I found was that the new commands did work for me.

Such as these as mentioned from Spiceworks:

“Start checking for updates: UsoClient StartScan

Start downloading Updates: UsoClient StartDownload

Start installing the downloaded updates: UsoClient StartInstall

Restart your device after installing the updates: UsoClient RestartDevice

Check, Download and Install Updates: UsoClient ScanInstallWait”

Then of course these as mentioned in the TechNet post:

“RefreshSettings – used to quickly enact any settings changes
RestartDevice – as the name implies, it restarts the device. Can be used in a script to allow updates to finish installing on next boot.
ResumeUpdate – used to tell the tool to resume updating after a reboot.
StartDownload – initiates a full download (from Microsoft) of existing updates
StartInstall – kicks-off the installation of the downloaded updates
ScanInstallWait – Combined Scan Download Install
StartInteractiveScan – we’ve yet to get this one to work, but it suggests that the process may work in a GUI
StartScan – kicks-off a regular scan”

While it is nice to see something available, it would be nice if MS made a more formal announcement of the deprecation and the replacements.

Hope this helps someone.

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Repair a Corrupted Windows Boot… Again

The Story

This one begins with a support request that a system is non responsive. The usual suggestion of a hard shutdown and reboot is suggested.
They responded that it was erroring with something else, then stated it would go into “attempting repair” and restart and this cycle would continue.
Once I got a hold of the laptop, I attempted a boot repair using the recovery apps from the Windows 10 boot options. After that failed I resorted to my old blog post: blog post with a similar problem from years ago, showed the same symptoms :
bootrec /FixMBR (didn’t work)
bootrec /FixBoot (access denied)
bootrec /ScanOS (Found 0 installed instances)
bootrec /RebuildBCD (Found 0 installed instances)
Quickly Googling the access denied on fixing brought me to this answers page on MS, where billy reminded be about assigning the boot partition a drive letter. As well as a newer command to run which worked!
1) Diskpart
2) List Vol
3) Select Vol (3 or 4, which ever is ~100MB)
4) Assign letter V
5) bcdboot C:\windows /s V: /f UEFI
.
I was pretty shocked to see Windows boot, and glad one system I didn’t have to re-image and manually save files. 😀
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Removing “Network” from File Explorer

SOURCE: Winareo

Update I wouldn’t recommend this way.

  1. Go to the following Registry key: 
    HKEY_CLASSES_ROOT\CLSID\{F02C1A0D-BE21-4350-88B0-7367FC96EF3C}\ShellFolder
  2. Set the value data of the DWORD value Attributes to b0940064.If you are running a 64-bit operating system, repeat the steps above for the following Registry key: 
    HKEY_CLASSES_ROOT\Wow6432Node\CLSID\{F02C1A0D-BE21-4350-88B0-7367FC96EF3C}}\ShellFolder

The Issue with this method is it requires you to take ownership of the key, usually by running regedit as system using psexec. I thought maybe if I created a GPO to deploy these  settings it would work, but instead got Error Code: 0x80070005, which apprently means access denied.

After farting around a bit down a rabbit hole about HKCR and how it’s apparently derived from HCLM\Software\Classes. I then decided to simply ask Google how to remove that icon via a GPO as much easier techniques usually exist. Where I found this Spice works thread post where a user by the name of Adam Sneed provided a adm file, which if you are unaware create configuration areas within GPMC to manage workstation. If you also know GPO’s generally when pushed down to client machines are nothing more then registry changes. So opening up the shared adm file from Adam shows the following:

CLASS User

CATEGORY !!Custom

CATEGORY !!ExplorerExtras

 POLICY !!HideNetworkInExplorer
 KEYNAME "SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\NonEnum"
 EXPLAIN !!HideNetworkInExplorer_Help
 VALUENAME "{F02C1A0D-BE21-4350-88B0-7367FC96EF3C}"
 VALUEON NUMERIC 1
 VALUEOFF NUMERIC 0
 END POLICY

END CATEGORY

END CATEGORY

[strings]
 Custom="Custom Policies"
 ExplorerExtras="Windows Explorer Extra's"
 HideNetworkInExplorer="Hide the Network Icon in Explorer 2008/Vista/Windows 7"
 HideNetworkInExplorer_Help="Enable this to hide the netowrk icon, disable or unconfigure to show the network icon."

As you can see the key we are interested in is “SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\NonEnum”

Checking it out manually on the client machine is HKLM, which I later found out is directly answered in this TechNet post.

Hive: HKEY_LOCAL_MACHINE
Key Path: SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\NonEnum
Value name: {F02C1A0D-BE21-4350-88B0-7367FC96EF3C}
Value type: REG_DWORD
Value Data (hex): 00000001

Doh

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WMIC Fun!

I’ve blogged about WMI before, more for setting up dedicated accounts for monitoring purposes.

Today we are going to have some fun with WMIC, the command line interface for simple and quick query data.

I got these ideas after reading this source blog… and I was curious at what level these worked (admin or not)

Using WMI

Most WMIC commands are issued in the following format:

wmic [Object Class] [Action] [Parameters]

For example, you can collect a list of groups or users on the local system and domain using the following commands:

wmic group list brief
wmic useraccount get name,sid

Yup, SIDs are no secret and you can pretty much query the whole domain if there’s been no hardening done. I haven’t tested this on a hardened domain but out of the box all users login name and SID are open for any standard user to query.

You can also perform the same data collection over the network without ever logging into the remote machine provided you know have some administrative credentials that the remote system will accept.

The same command issued against a remote system in another domain looks like this:

wmic /user:"FOREIGN_DOMAIN\Admin" /password:"Password" /node:192.168.33.25 group list brief

I can’t test this in my lab as I don’t have an alternative domain to play with (yet), but let’s see if I can query a member server using a standard domain account:

wmic /node:subca.zewwy.ca group list brief

nope well that’s good…

Processes
WMIC can collect a list of the currently running processes similar to what you’d see in “Task Manager” using the following command:

wmic process list
wmic process get name

Note that some of the WMIC built-ins can also be used in “brief” mode to display a less verbose output. The process built-in is one of these, so you could collect more refined output using the command:

wmic process list brief

Yup, those all work, even as standard user.

Some examples

Start an Application

wmic process call create "calc.exe"

Yeah… that worked…

I decided to see if I could somehow exploit these to get elevated rights, so far no dice.. but I did find this randomly while searching for a possible way…

sure enough, if you add start cmd.exe /k “net use” and name it net use.bat it will go into and endless loop. Mhmm interesting and easiest way to do a Denial Of Service attack.

anyway moving on…

System Information and Settings

You can collect a listing of the environment variables (including the PATH) with this command: (standard User works)

wmic environment list

OS/System Report HTML Formatted

wmic /output:c:os.html os get /format:hform

This was literally cause my standard account didn’t have access to C:\temp cause I created the folder using my admin account at some earlier point in time.

Products/Programs Installed Report HTML Formatted

wmic /output:c:product.html product get /format:hform

Turn on Remoted Desktop Remotely

Wmic /node:"servername" /user:"user@domain" /password: "password" RDToggle where ServerName="server name" call SetAllowTSConnections 1

Get Server Drive Space Usage Remotely (any node commands require elevated permissions, standard user fails at these generally)

WMIC /Node:%%A LogicalDisk Where DriveType="3" Get DeviceID,FileSystem,FreeSpace,Size /Format:csv MORE /E +2 >> SRVSPACE.CSV

Get PC Serial Number (works as standard user)

wmic bios get serialnumber

Get PC Product Number (works as standard user)

wmic baseboard get product

Find stuff that starts on boot (works as standard user)

wmic STARTUP GET Caption, Command, User

Reboot or Shutdown (works as standard user)

wmic os get buildnumber
wmic os where buildnumber="2600" call reboot

Get Startup List (works as standard user)

wmic startup list full

Information About Harddrives (works as standard user)

wmic logicaldisk where drivetype=3 get name, freespace, systemname, filesystem, size, volumeserialnumber

Information about OS (works as standard user)

wmic os get bootdevice, buildnumber, caption, freespaceinpagingfiles, installdate, name, systemdrive, windowsdirectory /format:htable > c:osinfo.htm

User and Groups

Local user and group information can be obtained using these commands:

wmic useraccount list
wmic group list
wmic sysaccount list

For domain controllers, this should provide a listing of all user accounts and groups in the domain. The “sysaccount” version provides you with system accounts built-in and otherwise,which is useful for any extra accounts that may have been added by rootkits.

Identify any local system accounts that are enabled (guest, etc.)

wmic USERACCOUNT WHERE "Disabled=0 AND LocalAccount=1" GET Name

Number of Logons Per USERID

wmic netlogin where (name like "%skodo") get numberoflogons

Get Domain Names And When Account PWD set to Expire

WMIC UserAccount GET name,PasswordExpires /Value

Patch Management

Need to know if there are any missing patches on the system? WMIC can help you find out with this command:

wmic qfe list

The QFE here stands for “Quick Fix Engineering”.
The results also include the dates of install should that be needed from an auditing standpoint.

Shares

Enumeration of all of the local shares can be collected using the command:

wmic share list

The result will also include hidden shares (named with a $ at the end).

Find user-created shares (usually not hidden)

wmic SHARE WHERE "NOT Name LIKE '%$'" GET Name, Path

so far all these are working as standard user, but that doesn’t mean anything.

Networking

Use the following command to extract a list of network adapters and IP address information:

wmic nicconfig list

Get Mac Address:

wmic nic get macaddress

Update static IP address:

wmic nicconfig get description, index
wmic nicconfig where index=9 call enablestatic("192.168.16.4"), ("255.255.255.0")

Yup got to be an admin for that one

Change network gateway:

wmic nicconfig where index=9 call setgateways("192.168.16.4", "192.168.16.5"),(1,2)

Enable DHCP:

wmic nicconfig where index=9 call enabledhcp

Get List of IP Interfaces

wmic nicconfig where IPEnabled='true'

Services

WMIC can list all of the installed services and their configurations using this command:

wmic service list

The output will include the full command used for starting the service and its verbose description.

Other examples

Service Management

 wmic service where caption="DHCP Client" call changestartmode "Disabled"

Look at services that are set to start automatically

wmic SERVICE WHERE StartMode="Auto" GET Name, State

Services Report on a Remote Machine HTML Formatted:

wmic /output:c:services.htm /node:server1 service list full / format:htable

Get Startmode of Services

Wmic service get caption, name, startmode, state

Change Start Mode of Service:

wmic service where (name like "Fax" OR name like "Alerter") CALL ChangeStartMode Disabled

Get Running Services Information

Wmic service where (state="running") get caption, name, startmode, state

Another interesting feature of WMIC is its ability to record the run-time command executed and runtime configuration all in one XML file. A recorded session might look something like this:

wmic /record:users_list.xml useraccount list

Of course, since WMIC wasn’t designed as a recording device, there are some caveats to using the XML. First, you can only use XML output, there are no other formats defined.

Event logs

Obtain a Certain Kind of Event from Eventlog

wmic ntevent where (message like "%logon%") list brief

Clear the Eventlog

wmic nteventlog where (description like "%secevent%") call cleareventlog

Retrieve list of warning and error events not from system or security logs

WMIC NTEVENT WHERE “EventType < 3 AND LogFile != ‘System’ AND LogFile != ‘Security’” GET LogFile, SourceName, EventType, Message, TimeGenerated /FORMAT:”htable.xsl”:” datatype = number”:” sortby = EventType” > c:appevent.htm

Thanks Andrea!

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NTFS Permissions and the Oddities

NTFS Permissions

What is NTFS?

NTFS is a high-performance and self-healing file system proprietary to Windows NT, 2000, XP, Vista, Windows 7, Windows 8, Windows 10 desktop systems as well as commonly used on Windows Servers 2016, 2012, 2008, 2003, 2000 & NT Server. NTFS file system supports file-level security, transactions, encryption, compression, auditing and much more. It also supports large volumes and powerful storage solution such as RAID/LDM. The most important features of NTFS are data integrity (transaction journal), the ability to encrypt files and folders to protect your sensitive data as well as the greatest flexibility in data handling.

Cool, now that we got that out of the way, file systems require access controls, believe it or not that’s controlled using lists called Access Control Lists (ACLs). Huh, who would of thunk it, ACLs either Allow or Deny permissions to the files and folders in the file system.

So far nothing odd or crazy here… There can come times when a user may have multiple permissions on a resource from alternative sources E.G. (Explicit vs Inherited), now depending which will determine whether the action is allowed or dined based on precedence.

A little more intricate, but still nothing odd here. However good reference material. Up Next, another tid bit required to understand the oddtites I will discuss.

File Explorer (explorer.exe)

If you’re an in-depth sysadmin you may know that by default (Windows7+) you can not run file explorer (explorer.exe) as an admin, or elevated. References one and two. Now in the second one there is a work around but I have not tested this, though I will actually probably for my next blog post. But for now the main thing to no is that you can’t run explorer elevated by default.

Turns out this is due to Explorer.exe being single threaded.. apparently.

Source One (says it’s possible, with person reply… didn’t work, links to source 2)

Source Two (Follow up initial question as to why it didn’t work, links to source 3)

Source Three (Old MS doc from unknown author with slight misconception based on my findings below.

“When running as a administrator with UAC enabled, your standard user token does not have write permissions to these protected folders.” –Correct

“Unfortunately, because Windows Explorer was not designed to run in multiple security contexts in the same desktop session, Windows cannot simply throw up a UAC prompt and then launch an elevated instance of Explorer.” –Correct

“Instead, you get one or more elevation prompts (if full-prompting is enabled) and Windows completes the operations using the full administrator token. This can be annoying if you have to make repeated operations in these folders.” –Slightly bad wording, it SHOULD simply utilize UAC prompt creds to complete the requested action (create folder, or navigate folder), but as shown below it will actually adjust the ACL’s themselves to let the action requested complete under the security context of the current running user.

Next! See all Examples of my claim as indicated in this blog post.

User Access Control (UAC)

So again talking WIndows 7 onward here Microsoft made NTFS more secure by having the OS utilize User Access Controls, for when elevated rights were required. For we all do best practices and use different admin and standard accounts, right? To keep it short the lil pop up asking “Are you sure you want to run this?” if you have the ability to run elevated or a Credential Pop-up dialog if you do not.

You can view the “Tasks that trigger a UAC prompt” section of the wiki to get an idea when. (Pretty much anytime you require an system level event)

However I’m going to bring attention this specific one:

Viewing or changing another user’s folders and files

Oddity #1

This brings up our first oddity. If I were to ask you the following question:

You are logged on as an admin on a workstation, you open file explorer, you navigate to a folder in which you do not have either explicit or inherited permissions. When you double click this folder you are presented with a UAC prompt, what does clicking “Continue” do?

A) Clicking Continue causes UAC to temperately runs explorer elevated and navigates into the folder.

B) Clicking Continue will take the current logged on user Security Identifier (SID) and append it to the folders ACL.

Now if you are following along closely we already discussed that A) isn’t even a viable option which means the answer is non other then B…

 

Yup, marvel at it… dirty ACLs everywhere. Now do note I had to break inheritance from the parent folder in order to restrict normal access, which makes sense when your navigating folders in file explorer as an admin already. But this information is still good to know if you do come across this when you are working in an elevated user session.

Also note IF the folder’s owner is SYSTEM or TrustedInstaller, clicking continue will not work and you’ll get an error, cause this action will not take ownership of a folder only grant access, and without the rights to grant those permissions it will still fail, even though there’s nothing stopping you from using takeown or the file explorer to actually grant your account ownership.

Oddity #2

This is the one I really wanted to cover in this blog post. You may have noticed that I stated I broke inheritance, this is generally not best practice and should be done as a last resort usually when it comes to permission management. However it does come around as a solution to access control when it really needs to be super granular.

I had created a TechNet post asking how to restore Volume ACLs, to which no good answers came about. So what I ended up doing was simply adding a new disk to a VM and checked out it’s permissions.

Now if you look closely you’ll notice 3 lines specifying specific access rights for the group “Users”. Now on a workstation, these permissions make perfect sense, a user has the right to read and execute files (needed just to use the system), create folders and they are the owners of them (what good is a workstation if you can’t organize your work), create files and write data (what goods a workstation if you can’t save your work).

However you might think, bah this will be a server (I’ll harden it that standard users can’t have interactive log on) so along with traversal bypass granted by default users should have access to only the specific folders in which they are explicitly granted, and by default will not have any access right inherited.

Removing Users still leaves the Administrators group with full Control rights, and you are a member of that group by domain inheritance, so all is good right? Sounds gravy until…. you realize as soon as you removed the “Users” accounts from the ACLs your admin account has inherited access rights revoked?

Inside the disk was a folder “Test” as you can see by its inherited ACLs

Now this is where it gets weird, it would be safe to assume that my domain admin account which I’m logged in as is part of the Built in administrators group… as demonstrated by this drawing here:

Which is also proven by the fact I can run CMD and other applications elevated via the UAC prompt and I simply click Yes instead of getting a credential box.

Now wouldn’t it be safe to assume that since Administrators have Full Control on the folder in question clearly shows that above, we should be able to traverse the folder, right? It’s basic operation of someone with “Full Control”… and…. awwwww would you look at that? Just look at it! Look at it!

It’s a big ol’ UAC prompt, now why would we get that if we have inherited permission… we already know what it’s going to do… that’s grant my account’s SID permissions, but why? I have inherited full control through administrators don’t I? and sure enough, clicking Continue…

well that’s super weird. I’m skip paste a lot of my trial and error tasks and make the claim, it literally comes down to one ACL that magically makes inheritance work like it’s suppose to…

believe it or not that’s it…. that’s the magical ACL on a folder that will make File Explorer actually adhere to inherited permissions. literally… granting S-1-5-32-545 Users “List folder \ Read Data” permission on the folder, and now as an admin I can traverse the folder without a UAC prompt, and without explicit permissions…

Oddity #3

So I’m like, alright, I’m liking this, I’m learning new things, things are getting weird…. and I can like weird, so I decided like YO! let’s create some folders and like see how things play out when I dickery do with those nasty little ACLs you know what I mean?

 

This stuffs too clean, you know what I mean, all nicely inherited, user owner, nah let’s change things up on this one, SYSTEM you got ownership, and you know what… all regular users.. yer gone you know what that means… inheritance who needs that. This is security, deeerrrrr…..

Awww yeah, and sure enough, trying to traverse the folder gives a UAC prompt, and grants my account explicit permissions, there goes those clean ACLs.

Answer to the Whole Thing

Turns out I was thinking about this all day at work, I couldn’t get it. It honest felt like somehow all access rights were being granted by the “Users” group only…. as if… they are.. using the lowest common denominator… like it can’t… run elevated! DOH!

The answer has been staring me in the face the whole freaking time!

I already stated “If you’re an in-depth sysadmin you may know that by default (Windows7+) you can not run file explorer (explorer.exe) as an admin, or elevated.”

I’m expecting to do task via explorer through an account I have inheritance from BUT the group I’m expecting to grant me the right is an elevated rights group “Administrators”… like DOH!

So the easy fix is create any random security group in the domain, add users accordingly into that group and grant that group full control over the folder, sub-folders and files (even make the group the owner of said folders and subfolders). Then sure enough everything works as expected.

For Example

added my admin account into this group. Then on the file server. Leave the D:\ disk permissions in place. Create a Folder in which other folders can be created and shared accordingly, in this case, teehee let’s call it DATA.

Sure enough, no surprise it looks like this…

everything as it should be, I created the Folder, my accounts the owner, I have inherited Full Control because I am the owner, and all other permissions have been granted by the base disk, besides the one permission which was configured at the disk level to be “this folder only” so all is good.

And now I did some quick searching on how to restrict access without breaking inheritance, and overall most responses was “even though it’s best practice to not break inheritance, alternative means for access control via deny’s is even more dirty”.

So, here we go lets break the inheritance from the disk and remove all users access, now as we discovered we will initially get UAC prompts if we try to navigate it with our admin account after this. Let’s not do that just yet after. So it’s now like this (we granted the group above ownership).

Now since I am a member of this group (I just added my account so I’m going to log off and back on to ensure my group mappings update properly for my kerberos tickets (TGT baby) to work.

whoami /groups

I’m so glad I did this, cause my MMC snap-in did not save the changes and I was not in this group after my first re-logon and sure enough after I fixed it.. 🙂

Now if I navigate the folder I should not get a UAC prompt cause my request to traverse the folder will be granted via File Share Admins, which is not an elevated SID request and I’ll be able to create files and folders without interruptions… lets try..

And there it is, no UAC prompt, all creation options available, and no users in the folders ACLs! Future Admins will need to be added to this group however, if an admin (domain admin or otherwise) attempts to login and navigate this folder they will get a UAC prompt and their SIDs will be auto appended to all folders, subfolders and files! Let me show you…

Welcome DeadUserAdmin! He’s been granted domain admin rights only, and decided to check out the file server…

as shown in the diagram the group permissions, and those inherited by simply being a domain admin, such as local admin. Below the permissions of a file before this domain admin attempts to navigate the folders..

Now as we learnt when this admin double clicks the DATA folder explorer can’t run elevated, and can’t grant traverse access via this accounts nested permissions under the administrators account, and when the UAC prompt appears is granting that SID direct access… lets follow:

There it is! and sure enough…

Yup every folder, and every file now has this SID in it, and when the user no longer works at the company…

SIDE ERROR****

deleting the Users Profile (to fix, naviagte in a couple folders, cut a folder, go to user profile root folder and paste to shorten the overall path name)

So anyway after the user leaves the company and his account gets deleted…

Yay, a whole entire folder/file structure with SIDs as Principals cause AD can’t resolve them anymore. They have been deleted. So how does an admin now fix DeadUserAdmins undesired effects?

Navigate to the root DATA folder properties, Security Tab, advanced settings. Remove the SID…

Be careful of the checkbox at the bottom (Replace all child permissions) use this with caution as it can do some damages if other folders down the line have broken inheritance and specific permissions. In this case all folders and files inherent from this base DATA drive and thus….

All get removed. If there are other folders with broken inheritance then an Audit is required of all folders, their resources, their purposes, and who’s suppose to have access.

Another option is to nest domain admins into file share admins, then it all works well too.

I hope this blog post has helped someone.

Posted on

Windows MCS and MPIO

I was configuring some iSCSI disk on a Windows server and noticed there were two different options available that seem to provide similar functionality and I had to know… What’s the difference?

Source

THE DIFFERENCE BETWEEN MCS AND MPIO (IN A NUTSHELL):

First we agree upon the common features within both technologies: both serve a multipathing for (iSCSI) I/O-operations utilizing multiple hardware (or OSI Level 1) components, such as Ethernet NICs or iSCSI HBAs. The purpose of multipathing is redundancy and aggregation – how this is implemented depends on the above depicted figures, i.e. through the decision which paths are active and which are passive (or standby, using Microsoft parlance). For the exact definition of the policies, such as round robin, weighted path, fail over only, etc. please refer to “MS iSCSI UG”, p. 41.

Finally here come the condensed definitions for both technologies:

MCS allows the initiator to establish multiple TCP/IP connections to the same target within the same iSCSI session.

MPIO in contrast allows the initiator to establish multiple iSCSI sessions (each having single TCP/IP connection) to the same target, effectively aggregating the duplicate devices into a single device.

If you are not familiar with the terminology (initiator, target, session, connection, initiator port and network portal) please refer to “Multivendor Post” which provides very informative sketches to the iSCSI network architecture.

Now that we know that MCS means effectively several connections within a session and MPIO means multiple sessions the question is when to use what. Mainly you will have to concentrate on two perspectives – vendor support and load balance policy inheritance. The question – or rather schools of thought – about the speed and performance differences are factored out here, because in the author’s opinion these are almost equal and you will probably never get to the point of fully utilizing them. With this said consider the following simple rule of thumb: you can use MCS only when it is supported from the vendor’s SAN and you are not using hardware iSCSI HBAs. In any other case use MPIO. The second thought is – if considering the above conditions you are able to use MCS, but want to apply different load balancing policies to different targets (and effectively LUNs or groups of LUNs) you will still be better off using MPIO. This is because load balancing policies are session adherent. In other words when you are applying policy to MCS it is for the whole session, no matter how many connections are aggregated “beneath” it. On the other side when using MPIO you can set different policies for different LUNs, because the multipathing is using different iSCSI sessions.

 

I’m still trying to wrap my hear around exactly what the source is getting at. But will update the blog when I do some more testing.

Posted on

CU update not Showing in WSUS

The Story

Today was a bit annoying…

I did my usual updates sync, and approve required updates, and in the past this has included CU’s without much fuss. However today I did my usual and ran check for updates on a member machine, returned clean (which i was expecting as per the results on WSUS console) and then I did the followup “Check for updates from Microsoft Updates” to my dismay the server stated an update was available a CU (KB4516061)… ughhh OK…

Checking WSUS

Decided to double check WSUS, to my dismay, re-syncing, and checking unapproved updates yielded no new updates. But I know there’s a new CU/// what gives?

Doing some reseach I find this is nothing really new and has been a problem for a while due to what could be multiple problems, including apparently packaging certain updates into other updates… how lovely.

As the main answer from that one says you can Import them… Ughhh fine…

*Expectation* Download MSU, click Import update, update gets imported to WSUS, and approve.

*Reality* Well reality is generally always worse then the expectations…

Importing Update into WSUS

So I downloaded the 1.5 Gig KB from MS Catalog and on my MMC snap-in click Import update… What do I get, a Windows Explorer popup asking me where the msu file I want to import is… NO… a link to the MS Catalog website…

Ughh… I already downloaded it what gives…

after a bit more research (honestly software should not be this non-intuitive, but that’s how old software was… non-intuitive…) turns out this “Import Updates” is not even designed for remote use (uhhh isn’t that the whole point of MMC Snap-ins?!?!?) Anyway, OK so people state you have to use it directly on the WSUS server….

FINE, Log directly into the server and open the WSUS console, click “Import Updates” IE opens and page can’t be loaded. Strange checking the IE security settings the site attempting to be navigated should be trusted.

Even grabbing the direct catalog link and pasting it in this IE window only gave me the option to Download, not “add” and then “view basket”. It turns out the option to add only becomes available after an ActiveX install for something.

Originally I was not getting this, it wasn’t until I read this , I found a golden egg on Technet, and very carefully read the answer:

MS WSUS Product Team:

“Just to let you know, a statement from the WSUS Product Team has been published: WSUS Catalog import failures

“We are aware of the issue and presently working on a fix. In the meantime, the following workarounds can be used to unblock your deployment:

After clicking on the “Import Updates…” option in the WSUS console, an Internet Explorer window will open on the following URL: http://catalog.update.microsoft.com/… &Protocol=1.20
Before proceeding with importing the updates, change the “1.20” protocol value in the URL to the previous protocol value “1.8”. The URL should look like this when you’re done: http://catalog.update.microsoft.com/… &Protocol=1.8″

Uhhh ok… so it turns out on the initial pop-up where you get the Windows can’t display this page:

Change end number to 1.8

Yes, and Yes

Once this page loads, you can add the Active X control at the bottom:

Now you get the add, and view basket, and finally get the import option:

Well that was an annoying morning…

And there they finally are…

Another annoying WSUS morning… :S *Update Feb 2020* still valid procedure.

Posted on

Update Computer Group Membership without Reboot

Source

Purge the computer account kerberos tickets

klist -lh 0 -li 0x3e7 purge

Force the gpo re-evaluation

gpupdate /force

Any previous attempt for access via newly added group membership should work; such as in this example I created a new Group, added this computer object into it, created a gMSA granting the group permission to use it, however the computer was not rebooted since added it into the group which was allowed access to install the gMSA.

PS C:\Windows\system32> New-ADGroup -Name "gMSANewGroup" -SamAccountName gMSANewGroup -GroupCategory Security -GroupScope Domain -DisplayName "gMSANewGroup" -Path "CN=Managed Service Accounts,DC=zewwy,DC=ca" -Description "Members of this group get Access to gMSATest2"
PS C:\Windows\system32> Add-ADGroupMember "gMSANewGroup" -Members "THISCOMP$"
PS C:\Windows\system32> New-ADServiceAccount -name gMSATest2 -DNSHostName gMSATest2.zewwy.ca -PrincipalsAllowedToRetrieveManagedPassword "gMSANewGroup"

Then Attempting to install the gMSA fails as the computer object hasn’t updated its group memberships locally, even though it has replicated throughout the domain, but following the command above to purge the computers tickets worked:

Hope this helps someone who needs to do granular group control but also don’t have the ability to reboot the host machine for service disruptions. 🙂

*NOTE* This does not apply to user group mapping. LSASS deal with users permission within groups (use whoami /groups) to see what I mean. a gpupdate /force, and a klist purge will not cause LSASS to update a users group membership. Users will still require to log off and back on for LSASS to apply new group memberships. Sorry!

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