Detection: Windows Devtunnels Image Loaded

Description

Detects image load events associated with Microsoft Devtunnels usage. Microsoft Devtunnels is a feature within Visual Studio that allows developers to expose their local development environment to the internet via secure, temporary tunnels, enabling external access for testing webhooks, APIs, and other services. While designed for legitimate development purposes, an attacker could exploit this feature to expose a compromised system or service to the internet, creating a covert communication channel that bypasses network security measures. By using Dev Tunnels, the attacker can establish a remote connection to the compromised environment, facilitate data exfiltration, or maintain command-and-control communications while avoiding detection by blending their activities with legitimate development traffic.

Search

 1`sysmon`
 2EventID=7
 3ImageLoaded="*\\AppData\\Local\\Temp\\.net\\devtunnel\\*"
 4ImageLoaded="*devtunnel.dll"
 5
 6| fillnull
 7
 8| stats count min(_time) as firstTime
 9              max(_time) as lastTime
10  by Computer ImageLoaded EventID loaded_file loaded_file_path process_exec process_guid
11     process_hash process_id process_name process_path service_dll_signature_exists
12     service_dll_signature_verified signature_id user_id vendor_product
13
14
15| rename Computer as dest
16
17| `security_content_ctime(firstTime)`
18
19| `security_content_ctime(lastTime)`
20
21| `windows_devtunnels_image_loaded_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 7	Windows	'XmlWinEventLog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

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

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Processes node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Legitimate developers using Microsoft Devtunnels for testing and debugging may trigger this detection. Filter alerts for approved development environments and personnel.

Associated Analytic Story

• Reverse Network Proxy

Risk Based Analytics (RBA)

Risk Message:

Potential Devtunnels image load observed on $dest$ via $ImageLoaded$.

References

• https://blueteamops.medium.com/detecting-dev-tunnels-16f0994dc3e2

Detection Testing

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: 1