Exchange PowerShell Module Usage

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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.

• Type: TTP

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2024-05-31
• Author: Michael Haag, Splunk
• ID: 2d10095e-05ae-11ec-8fdf-acde48001122

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1059	Command and Scripting Interpreter	Execution

T1059.001

PowerShell

Execution

Kill Chain Phase

• Installation

NIST

• DE.CM

CIS20

• CIS 10

CVE

Search

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

Macros

The SPL above uses the following Macros:

• powershell
• security_content_ctime

exchange_powershell_module_usage_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

• _time
• ScriptBlockText
• Opcode
• Computer
• UserID
• EventCode

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.

Known False Positives

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

Associated Analytic Story

• ProxyNotShell
• CISA AA22-277A
• ProxyShell
• BlackByte Ransomware
• CISA AA22-264A

RBA

Risk Score	Impact	Confidence	Message
32.0	40	80	Suspicious Exchange PowerShell module usaged was identified on $dest$.

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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
• 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/

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

source | version: 6