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

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Description

This analytic identifies suspicious behavior related to ProxyShell against on-premise Microsoft Exchange servers.
Modification of this analytic is requried to ensure fields are mapped accordingly.
A suspicious event will have PowerShell, the method POST and autodiscover.json. This is indicative of accessing PowerShell on the back end of Exchange with SSRF.
An event will look similar to POST /autodiscover/autodiscover.json a=dsxvu@fnsso.flq/powershell/?X-Rps-CAT=VgEAVAdXaW5kb3d... (abbreviated)
Review the source attempting to perform this activity against your environment. In addition, review PowerShell logs and access recently granted to Exchange roles.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel:
  • Last Updated: 2021-08-27
  • Author: Michael Haag, Splunk
  • ID: 29228ab4-0762-11ec-94aa-acde48001122

ATT&CK

ID Technique Tactic
T1190 Exploit Public-Facing Application Initial Access

| `exchange` c_uri="*//autodiscover.json*" cs_uri_query="*PowerShell*" cs_method="POST" 
| stats count min(_time) as firstTime max(_time) as lastTime by dest, cs_uri_query, cs_method, c_uri 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `exchange_powershell_abuse_via_ssrf_filter`

Associated Analytic Story

How To Implement

The following analytic requires on-premise Exchange to be logging to Splunk using the TA - https://splunkbase.splunk.com/app/3225. Ensure logs are parsed correctly, or tune the analytic for your environment.

Required field

  • _time
  • dest
  • cs_uri_query
  • cs_method
  • c_uri

Kill Chain Phase

  • Exploitation

Known False Positives

Limited false positives, however, tune as needed.

RBA

Risk Score Impact Confidence Message
80.0 80 100 Activity related to ProxyShell has been identified on $dest$. Review events and take action accordingly.

Reference

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: 1