:warning: THIS IS A EXPERIMENTAL DETECTION

This detection has been marked experimental by the Splunk Threat Research team. This means we have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.

Try in Splunk Security Cloud

Description

The following analytic detects suspicious behavior indicative of ProxyShell exploitation against on-premise Microsoft Exchange servers. It identifies HTTP POST requests to autodiscover.json containing PowerShell in the URI, leveraging server-side request forgery (SSRF) to access backend PowerShell. This detection uses Exchange server logs ingested into Splunk. Monitoring this activity is crucial as it may indicate an attacker attempting to execute commands or scripts on the Exchange server. If confirmed malicious, this could lead to unauthorized access, privilege escalation, or persistent control over the Exchange environment.

  • Type: TTP

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

  • Last Updated: 2024-05-21
  • Author: Michael Haag, Splunk
  • ID: 29228ab4-0762-11ec-94aa-acde48001122

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1190 Exploit Public-Facing Application Initial Access
T1133 External Remote Services Persistence, Initial Access
Kill Chain Phase
  • Delivery
  • Installation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


1
2
3
4
5



`exchange` c_uri="*//autodiscover*" 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:

:information_source: 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 fields

List of fields required to use this analytic.

  • _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.

:information_source: 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

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: 3