Detection: Exchange PowerShell Abuse via SSRF

EXPERIMENTAL DETECTION

This detection status is set to experimental. The Splunk Threat Research team has not yet fully tested, simulated, or built comprehensive datasets for this detection. As such, this analytic is not officially supported. If you have any questions or concerns, please reach out to us at research@splunk.com.

Updated Date: 2024-11-13 ID: 29228ab4-0762-11ec-94aa-acde48001122 Author: Michael Haag, Splunk Type: TTP Product: Splunk Enterprise Security

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.

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

Data Source

No data sources specified for this detection.

Macros Used

Name Value
exchange sourcetype="MSWindows:IIS"
exchange_powershell_abuse_via_ssrf_filter search *
exchange_powershell_abuse_via_ssrf_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1190 Exploit Public-Facing Application Initial Access
T1133 External Remote Services Initial Access
Delivery
Installation
DE.CM
CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

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

Risk Based Analytics (RBA)

Risk Message:

Activity related to ProxyShell has been identified on $dest$. Review events and take action accordingly.

Risk Object Risk Object Type Risk Score Threat Objects
dest system 80 No Threat Objects

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation Not Applicable N/A N/A N/A
Unit ❌ Failing N/A N/A N/A
Integration ❌ Failing N/A N/A N/A

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: GitHub | Version: 5