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.
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
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 firstname.lastname@example.org/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
Kill Chain Phase
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`
The SPL above uses the following Macros:
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.
List of fields required to use this analytic.
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
|80.0||80||100||Activity related to ProxyShell has been identified on $dest$. Review events and take action accordingly.|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
source | version: 1