Detection: Exchange PowerShell Module Usage

Description

The following analytic detects the usage of specific Exchange PowerShell modules, such as New-MailboxExportRequest, New-ManagementRoleAssignment, New-MailboxSearch, and Get-Recipient. It leverages PowerShell Script Block Logging (EventCode 4104) to identify these commands. This activity is significant because these modules can be exploited by adversaries who have gained access via ProxyShell or ProxyNotShell vulnerabilities. If confirmed malicious, attackers could export mailbox contents, assign management roles, conduct mailbox searches, or view recipient objects, potentially leading to data exfiltration, privilege escalation, or unauthorized access to sensitive information.

Search

1`powershell` EventCode=4104 ScriptBlockText IN ("*New-MailboxExportRequest*", "*New-ManagementRoleAssignment*", "*New-MailboxSearch*", "*Get-Recipient*", "Search-Mailbox") 
2| stats count min(_time) as firstTime max(_time) as lastTime by Opcode Computer UserID EventCode ScriptBlockText 
3| rename Computer as dest 
4|rename UserID as user 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `exchange_powershell_module_usage_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Powershell Script Block Logging 4104	Windows	'xmlwineventlog'	'XmlWinEventLog:Microsoft-Windows-PowerShell/Operational'	N/A

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

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.

Known False Positives

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

Associated Analytic Story

• BlackByte Ransomware

• CISA AA22-264A

• CISA AA22-277A

• ProxyNotShell

• ProxyShell

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/

Detection Testing

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

Source: GitHub | Version: 6