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Description

This search is to detect a suspicious attachment file extension in Gsuite email that may related to spear phishing attack. This file type is commonly used by malware to lure user to click on it to execute malicious code to compromised targetted machine. But this search can also catch some normal files related to this file type that maybe send by employee or network admin.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud, Dev Sec Ops Analytics
  • Datamodel:
  • Last Updated: 2021-08-16
  • Author: Teoderick Contreras, Splunk
  • ID: 6d663014-fe92-11eb-ab07-acde48001122

ATT&CK

ID Technique Tactic
T1566.001 Spearphishing Attachment Initial Access
T1566 Phishing Initial Access 
`gsuite_gmail` "attachment{}.file_extension_type" IN ("pl", "py", "rb", "sh", "bat", "exe", "dll", "cpl", "com", "js", "vbs", "ps1", "reg","swf", "cmd", "go") 
| eval phase="plan" 
| eval severity="medium" 
| 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 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `gsuite_email_suspicious_attachment_filter`

Associated Analytic Story

How To Implement

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.

Required field

  • _time
  • attachment{}.file_extension_type
  • attachment{}.sha256
  • destination{}.service
  • num_message_attachments
  • payload_size
  • subject
  • destination{}.address
  • source.address

Kill Chain Phase

  • Exploitation

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.

RBA

Risk Score Impact Confidence Message
49.0 70 70 suspicious email from $source.address$ to $destination{}.address$

Reference

Test Dataset

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

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