Windows Server USB File Write

Rule ID

PH_Rule_Change_23

Default Status

Enabled

Description

Detects Windows Server USB file writes

Severity

MITRE ATT&CK® Tactics

Exfiltration

Exfiltration consists of techniques that adversaries may use to steal data from your network. Once they’ve collected data, adversaries often package it to avoid detection while removing it. This can include compression and encryption. Techniques for getting data out of a target network typically include transferring it over their command and control channel or an alternate channel and may also include putting size limits on the transmission.

https://attack.mitre.org/tactics/TA0010

MITRE ATT&CK® Techniques

T1052.001

Exfiltration Over Physical Medium: Exfiltration over USB

Adversaries may attempt to exfiltrate data over a USB connected physical device. In certain circumstances, such as an air-gapped network compromise, exfiltration could occur via a USB device introduced by a user. The USB device could be used as the final exfiltration point or to hop between otherwise disconnected systems.

https://attack.mitre.org/techniques/T1052/001

Impacts

Application

Data Source

Windows FIM Via FortiSIEM Agent

Detection

Correlation

Remediation Guidance

Make sure it is an authorized change

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

Writes

SubPattern Definitions

SubPattern Name: Writes

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType IN ("AO-WUA-RemovableMedia-AddFile","AO-WUA-RemovableMedia-ModifyFile","AO-WUA-RemovableMedia-RemoveFile","AO-WUA-RemovableMedia-RenameFile")

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

reptDevName,diskName,fileName,osObjAction,user,domain

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT (*) >= 1

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

 hostName = Writes.reptDevName,
 diskName= Writes.diskName,
 fileName= Writes.fileName,
 osObjAction = Writes.osObjAction,
 user= Writes.user,
 domain= Writes.domain

FortiSIEM Rules