Process

1) Change lockout policy according to Microsoft Recommendation

The lockout policy’s ultimate goal is to protect against automated password guessing (brute-force attack) and as such, the value should be high enough so that accounts are not accidentally locked out by an end user or incorrect saved password.

As per the following articles, I would recommend the following lockout settings

• Account lockout threshold 50
• Reset account lockout counter after 10 minutes

https://technet.microsoft.com/en-us/library/cc671957(v=ws.10).aspx

https://technet.microsoft.com/en-us/library/hh994574(v=ws.11).aspx

2) Enabling Auditing

Identifying the source of the account lockouts in a complex environment will be virtually impossible without auditing enabled.

Please note: Only events that occurred after enabling auditing will be logged. It also might be necessary to increase Security log file size

In addition to the above, the following might provide some extra clues to the source of the lockout. After setting these values, additional logs can be found in Event Viewer, Applications and Services Log/Microsoft/Windows/NTLM

Path: Computer Configuration\Windows Settings\Local Policies\Security Options
Setting: Network Security: Restrict NTLM: Audit Incoming NTLM Traffic
Value: Enable auditing for all accounts
Setting: Network security: Restrict NTLM: Audit NTLM authentication in this domain
Value:    Enable All

3) Identify source device that lockout occurred on

3.1) Event Comb

Part of Account Lockout and Management Tools https://www.microsoft.com/en-us/download/details.aspx?id=18465

Still a useful tool in a pinch.

Please note: Built-in search for account lockout is not using the newer event IDs. To search newer IDs, add 4625 4740 4771 4768 4776 to the list

For details on these events, see

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=529

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=4625

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=644

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=4740

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=675

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=4771

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=676

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=4768

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=681

https://www.ultimatewindowssecurity.com/securitylog/encyclopedia/event.aspx?eventid=4776

All gathered events from selected domain controllers will be saved into text files in the temp folder

3.2) Lockout Status

Part of Account Lockout and Management Tools https://www.microsoft.com/en-us/download/details.aspx?id=18465

When you start tool you specify the user account to inspect.

Please note: If the lock device is a Domain Controller, you have to follow the trail until you get to the actual source device name

3.3) AD Audit

See https://www.manageengine.com/products/active-directory-audit

My personal favorite, AD Audit makes finding the source account that locks device super easy, just use built-in reports

4.1) Powershell

FindUserBadPwdAttempts

https://gallery.technet.microsoft.com/Troubleshoot-Account-Bad-4bf47940

Get-LockedOutLocation

https://gallery.technet.microsoft.com/scriptcenter/Get-LockedOutLocation-b2fd0cab

4) Identify the source process that locked the account

4.1) NetWrix Account Lockout Examiner

See https://www.netwrix.com/account_lockout_examiner.html

Install NetWrix Account Lockout Examiner on another computer. After that run it and point to the device that generates lockouts.

4.2) ADAudit

See https://www.manageengine.com/products/active-directory-audit

As I said before, my personal favorite. After finding source account that locks device using built-in reports, the Account Lockout Analyzer can show the source process that locks accounts

5) Implement processes to prevent future lockouts

5.1 Windows Services, Scheduled Tasks and COM Objects

Utilize service accounts with strong non-expiring passwords or managed service accounts.

5.2 Drive Mappings

Do not map drives with explicit username and password. Utilize Group Policy User Drive Map Preference to map the drive mappings.

5.3 Logon Sessions

Implement RDP inactive/idling session logoff.

5.4 LAN Manager Authentication Level

Ensure that your LAN Manager Authentication Level is at the required level for your clients and authentication used.

5.5 Externally Exposed RDP

Install a tool such as RDP Guard to automatically block external brute-force attacks or better yet, set up a secure VPN and access RDP from within this VPN

5.6 Credential Manager

Disable the Credential Manager service. This will prevent users from saving/using stored passwords

5.7 Cached Credential

Remove cached credentials for both user and SYSTEM accounts

For user accounts

rundll32.exe keymgr.dll,KRShowKeyMgr

For SYSTEM accounts

psexec -s -i -d rundll32.exe keymgr.dll,KRShowKeyMgr

Tips

If your account that you are using for the investigation is locking, rename your username for the duration of the investigation