ID | Technique | Tactic |
---|---|---|
T1190 | Exploit Public-Facing Application | Initial Access |
T1133 | External Remote Services | Initial Access |
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.
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.
Search
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
Name | Platform | Sourcetype | Source | Supported App |
---|---|---|---|---|
N/A | N/A | N/A | N/A | N/A |
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
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 |
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 | Risk Score | Impact | Confidence |
---|---|---|---|
Activity related to ProxyShell has been identified on $dest$. Review events and take action accordingly. | 80 | 80 | 100 |
References
-
https://github.com/GossiTheDog/ThreatHunting/blob/master/AzureSentinel/Exchange-Powershell-via-SSRF
-
https://blog.orange.tw/2021/08/proxylogon-a-new-attack-surface-on-ms-exchange-part-1.html
-
https://peterjson.medium.com/reproducing-the-proxyshell-pwn2own-exploit-49743a4ea9a1
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: 3