WARNING THIS IS A EXPERIMENTAL object

We have not been able to test, simulate, or build datasets for this object. Use at your own risk. This analytic is NOT supported.

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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

  • Last Updated: 2021-08-27
  • Author: Michael Haag, Splunk
  • ID: 29228ab4-0762-11ec-94aa-acde48001122

Annotations

ATT&CK
ID Technique Tactic
T1190 Exploit Public-Facing Application Initial Access
Kill Chain Phase
  • Exploitation
NIST
CIS20
CVE
1
2
3
4
5
6
| `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`

Macros

The SPL above uses the following Macros:

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

Required field

  • _time
  • dest
  • cs_uri_query
  • cs_method
  • c_uri

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.

Known False Positives

Limited false positives, however, tune as needed.

Associated Analytic story

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