Windows Exchange PowerShell Module Usage

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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).
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).

• Type: TTP

• Product: Splunk Behavioral Analytics

• Last Updated: 2022-10-12
• Author: Michael Haag, Splunk
• ID: 1118bc65-b0c7-4589-bc2f-ad6802fd0909

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

 
| from read_ba_enriched_events() 
| eval timestamp = ucast(map_get(input_event,"time"),"long", null) 
| eval metadata = ucast(map_get(input_event, "metadata"),"map<string, any>", null) 
| eval metadata_uid = ucast(map_get(metadata, "uid"),"string", null) 
| eval device=ucast(map_get(input_event,"device"), "map<string, any>", null) 
| eval device_hostname=ucast(map_get(device,"hostname"), "string", null) 
| eval process=ucast(map_get(input_event,"process"), "map<string, any>", null) 
| eval process_file=ucast(map_get(process,"file"), "map<string, any>", null) 
| eval process_file_path=ucast(map_get(process_file,"path"), "string", null) 
| eval process_uid=ucast(map_get(process,"uid"), "string", null) 
| eval process_cmd_line=ucast(map_get(process,"cmd_line"), "string", null) 
| eval actor=ucast(map_get(input_event,"actor"), "map<string, any>", null) 
| eval actor_user=ucast(map_get(actor,"user"), "map<string, any>", null) 
| eval actor_user_uid=ucast(map_get(actor_user,"uid"), "string", null) 
| where match_regex(process_cmd_line, /(?i)get-recipient/)=true OR match_regex(process_cmd_line, /(?i)new-mailboxsearch/)=true OR match_regex(process_cmd_line, /(?i)new-managementroleassignment/)=true OR match_regex(process_cmd_line, /(?i)new-mailboxexportrequest/)=true --finding_report--

Macros

The SPL above uses the following Macros:

windows_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.

• device.hostname
• process.file.path
• process.uid
• process.cmd_line
• actor.user.uid

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. 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

RBA

Risk Score	Impact	Confidence	Message
32.0	40	80	Exchange enumeration using PowerShell on $dest_device_id$.

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

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