Detection: Windows Exchange PowerShell Module Usage

Description

The following analytic identifies the usage of Exchange PowerShell modules that were recently used for a proof of concept related to ProxyShell. Currently, there is no active data shared or data we could re-produce relate to this part of the ProxyShell chain of exploits. Inherently, the usage of the modules is not malicious, but reviewing parallel processes, and user, of the session will assist with determining the intent. Module - New-MailboxExportRequest will begin the process of exporting contents of a primary mailbox or archive to a .pst file. Module - New-managementroleassignment can assign a management role to a management role group, management role assignment policy, user, or universal security group (USG). Module - New-MailboxSearch cmdlet to create a mailbox search and either get an estimate of search results, place search results on In-Place Hold or copy them to a Discovery mailbox. You can also place all contents in a mailbox on hold by not specifying a search query, which accomplishes similar results as Litigation Hold. \ Module - Get-Recipient cmdlet to view existing recipient objects in your organization. This cmdlet returns all mail-enabled objects (for example, mailboxes, mail users, mail contacts, and distribution groups).

Annotations

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Implementation

To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell. This will only work with Multiline event logs, not XML.

Known False Positives

Administrators or power users may use this PowerShell commandlet

Associated Analytic Story

• ProxyShell

• CISA AA22-264A

Risk Based Analytics (RBA)

References

• https://docs.microsoft.com/en-us/powershell/module/exchange/new-mailboxexportrequest?view=exchange-ps

• https://docs.microsoft.com/en-us/powershell/module/exchange/new-managementroleassignment?view=exchange-ps

• https://blog.orange.tw/2021/08/proxyshell-a-new-attack-surface-on-ms-exchange-part-3.html

• https://www.zerodayinitiative.com/blog/2021/8/17/from-pwn2own-2021-a-new-attack-surface-on-microsoft-exchange-proxyshell

• https://thedfirreport.com/2021/11/15/exchange-exploit-leads-to-domain-wide-ransomware/

• https://www.cisa.gov/uscert/ncas/alerts/aa22-264a

• https://learn.microsoft.com/en-us/powershell/module/exchange/new-mailboxsearch?view=exchange-ps

• https://learn.microsoft.com/en-us/powershell/module/exchange/get-recipient?view=exchange-ps

• https://thedfirreport.com/2022/03/21/apt35-automates-initial-access-using-proxyshell/

Version: 4