File added to the system through external media

You might need to identify files that were downloaded from removable media, such as a USB stick, when doing the following:

• Investigating a ransomware attack

Prerequisites 

In order to execute this procedure in your environment, the following data, services, or apps are required:

• Operating system event data

Example

A user plugged a USB stick into his machine. You suspect that the files the user downloaded from the USB stick are malicious and want to identify them.

NOTE: To optimize the search shown below, you should specify an index and a time range. In addition, this sample search uses Sysmon data. You can replace this source with any other operating system event data used in your organization.

1. Set the search time range to the date the user inserted the USB stick, if known.
2. Run the following search:

sourcetype=XmlWinEventLog:Microsoft-Windows-Sysmon/Operational host=<hostname> (CommandLine="d:\\*" OR ParentCommandLine="d:\\*")
|table _time CommandLine ParentCommandLine
|sort _time

Search explanation

The table provides an explanation of what each part of this search achieves. You can adjust this query based on the specifics of your environment.

Result

The files found in the results are those downloaded from the USB stick. Look for known suspicious file types. For example, malware authors sometimes use the .dotm Microsoft Word format because of the ability to embed macros and other scripts within it.