Windows 10: SMB file servers keep asking for credentials

Livy Inverse · Apr 22, 2019

I have both Windows 10 SMB and Linux Samba file servers. The share permissions are:

browsable (Linux) / turn on file and printer sharing (Windows)

guest ok (Linux) / turn off password protected sharing (Windows)

Appropriate file system level permissions on both servers (not really matters here)

Most of the time, using a Windows 10 client to connect to the shared folder is straight forward, just \\my-server and it is fine. But sometimes, it keep asking for credentials for unknown reason.

It won't connect if I leave all fields blank. Sometimes I need to type a random user account with a blank password, and sometimes both a random account plus a random password to pass that stupid prompt. Linux clients do not suffer from that issue, at least by using smb://my-server on Ubuntu's Nautilus and select Connect anonymously.

To make the problem worse, let's say I have a shared printer on the server. After a client provides a random user + password, he can connect to the server and use the shared printer. After a few days, he suddenly cannot print using the previously added printer, until he tries to connect and provides a random user + password again (the printer does not need to be re-added). Looks like the junk user + password time out after a few days (even if you do check Remember my credentials).

I've forwarded the port to my test server, so you can try to connect to it using \\113.178.30.205 , although I can't guarantee it will ask you for credentials. The issue occurs randomly. What could be the cause of the problem?

:)

Brink · Apr 22, 2019

Credential Guard lab companion

If you have heard about Credential Guard in Windows Server 2016 (and in Windows 10), but do not have an environment to try it out, here is a lab environment we built for you to play.

Lab access

The link will lead you to a sign up page, after that, you will see the following labs listed for Windows Server 2016:

Windows Server 2016 labs

There are 3 exercises in the “Implementing Breach Resistance Security in Windows Server 2016”:

Credential Guard

Remote Credential Guard

Device Guard

This blogpost will walk you through the Credential Guard lab details.

After click on the link of Breach Resistance lab, you be required to sign in and then you can launch the lab:

Sign-in

Launch page

It takes a few minutes to create the VMs, and once it has done, you will see the following machines prepared:

Initialize

DC: domain controller, which is not used for this exercise.

SRV01 and SRV02: both are Windows Server 2016, and used for the lab exercise.

Lab exercise – Explained

The steps are listed in the Content section:

Content

This lab is structured to cover the following in sequence:

Understand how attackers can use the hash in memory to gain access to domain controllers

Configure Credential Guard

Verify the hash in memory is protected using Credential Guard

You can follow the steps listed under the content section to complete the lab, the intent of the blog, is to break the procedures into groups, to help you understand the exercise better.

Prep the hash

Lsass.exe is the process which handles user logon, it stores the user credential information in its memory. The memory is cleared when the machine starts up. In this lab environment, all the virtual machines start at the time lab launches, when you logon to the machine, you will only have the logon user credential information in memory. In order to demonstrate an attacker gaining user access using other account’s hash, the first part of the lab is to simulate a server which has been running for a while, different users had remotely or locally connected to it, therefore, lsass memory stored many different user credential information.
This is accomplished by step 1-8.

Retrieving credential hash

Mimikatz is a popular tool for retrieving lsass memory information. The tool has been copied to the lab machines, step 9-13 walk you through the process of dumping lsass memory using Mimikatz.

Pass the Hash

Pass the hash is a hacking technique that allows an attacker to authenticate by using the underlying NTLM, instead of specifying the user password. In step 14 to 24, you will extract LabAdmin hash from lsass using Mimikatz, and use the hash to open a PowerShell console, and perform a couple of operations using the LabAdmin privilege:

Add a user to the domain admin group

Open remote PowerShell connection to a domain controller

Both operations could not be performed by the logon user. But using the hash of the LabAdmin, an attacker will be able to do it using the information retrieve from Lsass memory.

Configure and verify Credential Guard

Step 25 to 36 illustrate the steps to configure credential guard, then verify its status using msinfo32.exe and PowerShell.

Step 37 to 43 goes further to use Mimikatz to show the hash in Lsass is now encrypted using Credential Guard.

More info

The exercise illustrated the benefit of Credential Guard in Windows Server 2016 as well as Windows 10. For more information, you can find here.
Click to expand...

Source: Credential Guard lab companion Datacenter and Private Cloud Security Blog

See also:

Enable or Disable Credential Guard in Windows 10 Windows 10 Security System Tutorials

Verify if Credential Guard is Enabled or Disabled in Windows 10 Windows 10 Security System Tutorials

Am* · Apr 22, 2019

Uber file server build -- suggestions

Uber file server build -- suggestions?

I'm currently in the process of buying stuff for my file server build. Going to try and keep this build all in one thread this time.

Stuff already bought:

Motherboard (socket 1155 H61)
RAM (1600MHz)
PCI SATA cards
Operating System (Windows 8 + FreeNAS)
SSD
CPU (35w Pentium Ivybridge 2.6GHz)

Looking for suggestions on:

GPU -- use the on-die GPU or buy a PCI-E graphics card (was thinking of a 7750)? My only requirement is that it is able to run 1080p mkv files and play Blurays without a problem.
Case -- needs to hold as many 3.5" drives as humanly possible (more than 10 at least), while not being too expensive
PSU -- needs to be able to run over 40 SATA HDDs as well as 6xPCI RAID cards and 1xPCI-E 2.0 RAID card. Silver, Gold or Platinum?
CPU Cooler -- fanless or not?
Case fans

That's all I can think of for now...unless I'm forgetting something...oh and one more thing -- I will be buying the hard drives two at a time as I run out of space. Also the PCI-E RAID card will be bought a lot later down the line, as I've only just got enough hard drives for 1 out of 6 of my PCI SATA cards.

Any suggestions, feel free to post. Thanks

Dharmendra kumarsharma · Apr 22, 2019

SMB server in High availability

Hi ,

i am planning to deploy SMB server in our company,we have 1500 end users which is connected to our domain,i have two side DC and DR.so main concern is i want deploy SMB server in high availability,but i am not sure how to dont, know more about of this technical
specification .

Details below for deployment

1.Windos 2016 server std

2.Virtualization

3.External Storage

Windows 10: SMB file servers keep asking for credentials

SMB file servers keep asking for credentials

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