Agent FIM: Windows File Changed From Baseline

Rule ID

PH_Rule_Change_32

Default Status

Enabled

Description

FortiSIEM Windows Agent FIM detected that a file changed from its baseline

Severity

MITRE ATT&CK® Tactics

Defense Evasion

Defense Evasion consists of techniques that adversaries use to avoid detection throughout their compromise. Techniques used for defense evasion include uninstalling/disabling security software or obfuscating/encrypting data and scripts. Adversaries also leverage and abuse trusted processes to hide and masquerade their malware. Other tactics’ techniques are cross-listed here when those techniques include the added benefit of subverting defenses.

https://attack.mitre.org/tactics/TA0005

MITRE ATT&CK® Techniques

T1070.004

Indicator Removal on Host: File Deletion

Adversaries may delete files left behind by the actions of their intrusion activity to minimize the adversary's footprint. Tools such as cmd functions such as DEL, secure deletion tools such as Windows Sysinternals SDelete, or other third-party file deletion tools can be used.

https://attack.mitre.org/techniques/T1070/004

T1565.001

Data Manipulation: Stored Data Manipulation

Adversaries may insert, delete, or manipulate data at rest in order to manipulate external outcomes or hide activity. Stored data could include a variety of file formats, such as Office files, databases, stored emails, and custom file formats. By manipulating stored data, adversaries may attempt to affect a business process, organizational understanding, and decision making.

https://attack.mitre.org/techniques/T1565/001

Impacts

Server

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.

File

SubPattern Definitions

SubPattern Name: File

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 = "AO-WUA-FileMon-BaselineChange"

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,fileName,user,hashCode,targetHashCode,hashAlgo

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=File.reptDevName,
 fileName=File.fileName,
 user=File.user,
 hashCode=File.hashCode,
 targetHashCode=File.targetHashCode,
 hashAlgo=File.hashAlgo

FortiSIEM Rules