Tag Archive: Microsoft 365 Defender

Taking actions on on-prem accounts with MDI Action Account, troubleshooting

Background

The response action of blocking a compromised account is important to have available. Regardless of solution one must be able to quick and easy be able to block an account.  In MDI (part of Microsoft 365 Defender) it is possible since some time ago to configure an MDI Action Account, lately the option to run with the system account of the Domain Controller has been added to this feature and therefor you don’t have to configure the gMSA account.

Using system or a custom gMSA account

The choice is made based on organizational structure, Tiering/RBAC, MSSP partner. Basically, if you are required to delegate the permissions to only allow actions on accounts in certain OU’s, then you must use a custom gMSA accounts.

For example, if you have a MSSP partner monitoring your security and take actions to discovered threats, a so called MDR (Managed Detection and Response), you have an option to control to which accounts the MSSP can take actions.

The available actions are:

  • Disable user in Active Directory: This will temporarily prevent a user from logging in to the on-premises network. This can help prevent compromised users from moving laterally and attempting to exfiltrate data or further compromise the network.
  • Suspend user in Azure Active Directory: This will temporarily prevent a user from logging in to Azure Active Directory. This can help prevent compromised users from attempting to exfiltrate data and minimizes the time between Disable user in Active Directory and the sync of this status to the cloud.
  • Reset user password – This will prompt the user to change their password on the next logon, ensuring that this account can’t be used for further impersonation attempts.

From an MSSP perspective, this feature is very useful since there wouldn’t require customer access (VPN or other kind of access) to respond to threats. Even though this feature is very popular for MSSPs, you will still want to have this option if you have your internal security operations to be able to respond from the portal you are currently working in.

Even though this feature is very popular for MSSPs

To learn how to create and configure the gMSA account you can start with this link
https://learn.microsoft.com/en-us/defender-for-identity/manage-action-accounts

Troubleshooting

(The troubleshooting path will be updated based on troubleshooting session done with customers)

There 2 primary sources for troubleshooting this, sensor logs and event logs. Preferably the logs are sent to SIEM solution (like Microsoft Sentinel).

Using Sentinel (or look in the event viewer, or if you have another SIEM solution in place).

SecurityEvent | where Account has "gMSA-MDIAction$"

Note the $ character in the account name, gMSA account is more like a computer account. It’s the type of msDS-GroupManagedServiceAccount.

If the account doesn’t have logons ending with a $ (like a computer account), then it’s not a gMSA account and start there by creating a one.

https://learn.microsoft.com/en-us/defender-for-identity/manage-action-accounts

This can also be checked on the logon event (this will trigger 4625, logon failed)

Verify that the AccountType is “Machine”

Successful sign-in:

Account is not allowed to logon as a service

If the gMSA Account is setup and configured correctly and there is still event 4625 being logged.

Check the Status property of the login event

0xc000015b indicates that the account is not allowed to login0xC000015B

STATUS_LOGON_TYPE_NOT_GRANTED, A user has requested a type of logon (for example, interactive or network) that has not been granted. An administrator has control over who can logon interactively and through the network.

More information about the Status property can be found here:

https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4625

https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-erref/596a1078-e883-4972-9bbc-49e60bebca55

To address this issue you need to create a new or update existing policy to allow that account to logon as service on the target system (the DCs)

https://learn.microsoft.com/en-us/system-center/scsm/enable-service-log-on-sm?view=sc-sm-2022#enable-service-log-on-through-a-local-group-policy

Successful events effecting the user you try to take action on

The following query will find events of enabling and disabling a user

SecurityEvent
| where EventID in(4738,4725,4722)
| where Account contains "gMSA-mdi-action$"
| where TargetAccount contains "test" //the user you want to take action on
You see 4738 “A user account was changed” at the same timestamp as the 4725 and 4722 and the 4738 event show the UAC 0x10: Account Enabled and 0x11: Account Disabled

https://learn.microsoft.com/en-us/windows/security/threat-protection/auditing/event-4738

Hope this helps!

We will continue to update this post if we run into other related troubleshootings

//Happy Hunting

Take actions from Threat Hunting in M365 Defender

We wrote a blog post earlier about the news in threat hunting

New features in Advanced Hunting – Microsoft 365 Defender – SEC-LABS R&D

Another feature in hunting, which will speed up responses from a threat hunting scenario is Take Action

When selecting a record in the result, the Take Action button will be visible as seen in below picture

take actions, m365 defender

So instead of just creating a new incident or adding events to an existing incident we can take actions from the hunting experience.

In the Take actions experience we have actions grouped by Devices, Files and Users.

actionable items, m365 defender

The action options available is dependent on the data in the result. For instance, file information like checksum is required to being able to quarantine a file.

When clicking Next we can see the target selected and click Next

We can add a Remediation name and Description for our action

This feature enables a rapid response at the fingertips of the threat hunters for immediate actions

For further information, please visit

https://docs.microsoft.com/en-us/microsoft-365/security/defender/advanced-hunting-take-action?view=o365-worldwide

Happy Hunting!

Sec-Labs Team