Detection: GSuite Email Suspicious Attachment

Updated Date: 2024-09-30 ID: 6d663014-fe92-11eb-ab07-acde48001122 Author: Teoderick Contreras, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects suspicious attachment file extensions in GSuite emails, potentially indicating a spear-phishing attack. It leverages GSuite Gmail logs to identify emails with attachments having file extensions commonly associated with malware, such as .exe, .bat, and .js. This activity is significant as these file types are often used to deliver malicious payloads, posing a risk of compromising targeted machines. If confirmed malicious, this could lead to unauthorized code execution, data breaches, or further network infiltration.

Search

1`gsuite_gmail` "attachment{}.file_extension_type" IN ("pl", "py", "rb", "sh", "bat", "exe", "dll", "cpl", "com", "js", "vbs", "ps1", "reg","swf", "cmd", "go") 
2| eval phase="plan" 
3| eval severity="medium" 
4| stats count min(_time) as firstTime max(_time) as lastTime values(attachment{}.file_extension_type) as email_attachments, values(attachment{}.sha256) as attachment_sha256, values(payload_size) as payload_size by destination{}.service num_message_attachments  subject destination{}.address source.address phase severity 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `gsuite_email_suspicious_attachment_filter`

Data Source

Name	Platform	Sourcetype	Source
G Suite Gmail	N/A	`'gsuite:gmail:bigquery'`	`'http:gsuite'`

Macros Used

Name	Value
gsuite_gmail	`sourcetype=gsuite:gmail:bigquery`
gsuite_email_suspicious_attachment_filter	`search *`

gsuite_email_suspicious_attachment_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1566.001	Spearphishing Attachment	Initial Access
T1566	Phishing	Initial Access

KillChainPhase.DELIVERY

NistCategory.DE_AE

Cis18Value.CIS_10

APT-C-36

APT1

APT12

APT19

APT28

APT29

APT30

APT32

APT33

APT37

APT38

APT39

APT41

Ajax Security Team

Andariel

BITTER

BRONZE BUTLER

BlackTech

CURIUM

Cobalt Group

Confucius

DarkHydrus

Darkhotel

Dragonfly

EXOTIC LILY

Elderwood

FIN4

FIN6

FIN7

FIN8

Ferocious Kitten

Gallmaker

Gamaredon Group

Gorgon Group

Higaisa

Inception

IndigoZebra

Kimsuky

Lazarus Group

LazyScripter

Leviathan

Machete

Malteiro

Mofang

Molerats

Moonstone Sleet

MuddyWater

Mustang Panda

Naikon

Nomadic Octopus

OilRig

PLATINUM

Patchwork

RTM

Rancor

RedCurl

Saint Bear

Sandworm Team

SideCopy

Sidewinder

Silence

Star Blizzard

TA2541

TA459

TA505

TA551

The White Company

Threat Group-3390

Tonto Team

Transparent Tribe

Tropic Trooper

WIRTE

Windshift

Winter Vivern

Wizard Spider

admin@338

menuPass

Axiom

GOLD SOUTHFIELD

INC Ransom

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 Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search, you need to be ingesting logs related to gsuite having the file attachment metadata like file type, file extension, source email, destination email, num of attachment and etc.

Known False Positives

network admin and normal user may send this file attachment as part of their day to day work. having a good protocol in attaching this file type to an e-mail may reduce the risk of having a spear phishing attack.

Associated Analytic Story

Dev Sec Ops

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Suspicious email from $source.address$ to $destination{}.address$	49	70	70

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

https://www.redhat.com/en/topics/devops/what-is-devsecops

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`http:gsuite`	`gsuite:gmail:bigquery`
Integration	✅ Passing	Dataset	`http:gsuite`	`gsuite:gmail:bigquery`

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