splunk-security_content/docs/_posts/2021-08-27-exchange_powershell_module_usage.md

title, excerpt, categories, last_modified_at, toc, tags

title	excerpt	categories	last_modified_at	toc	tags
Exchange PowerShell Module Usage	PowerShell	Endpoint	2021-08-27	true	TTP T1059.001 PowerShell Execution Splunk Enterprise Splunk Enterprise Security Splunk Cloud Reconnaissance Exploitation

⚠️ WARNING THIS IS A EXPERIMENTAL DETECTION

We have not been able to test, simulate or build datasets for it, use at your own risk!

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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).

• Type: TTP
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel:
• Last Updated: 2021-08-27
• Author: Michael Haag
• ID: 2d10095e-05ae-11ec-8fdf-acde48001122

ATT&CK

ID	Technique	Tactic
T1059.001	PowerShell	Execution

Search

`powershell` EventCode=4104 Message IN ("*New-MailboxExportRequest*", "*New-ManagementRoleAssignment*") 
| stats count min(_time) as firstTime max(_time) as lastTime by Path Message OpCode ComputerName User EventCode
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `exchange_powershell_module_usage_filter`

Associated Analytic Story

• ProxyShell

How To Implement

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.

Required field

• _time
• Path
• Message
• OpCode
• ComputerName
• User
• EventCode

Kill Chain Phase

• Reconnaissance
• Exploitation

Known False Positives

Administrators or power users may use this PowerShell commandlet for troubleshooting.

RBA

Risk Score	Impact	Confidence	Message
15.0	30	50	Local user discovery enumeration using PowerShell on dest by user

Reference

• 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

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

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