:warning: THIS IS A EXPERIMENTAL DETECTION

This detection has been marked experimental by the Splunk Threat Research team. This means we have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.

Try in Splunk Security Cloud

Description

This search can help the detection of compromised accounts or internal users sending suspcious calendar invites via GSuite calendar. These invites may contain malicious links or attachments.

  • Type: Hunting

  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

  • Last Updated: 2021-10-24
  • Author: Rod Soto, Teoderick Contreras
  • ID: 03cdd68a-34fb-11ec-9bd3-acde48001122

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1566 Phishing Initial Access
Kill Chain Phase
  • Delivery
NIST
  • DE.AE
CIS20
  • CIS 10
CVE 


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`gsuite_calendar` 
|bin span=5m _time 
|rename parameters.* as * 
|search target_calendar_id!=null email="*yourdomain.com"
| stats  count values(target_calendar_id) values(event_title) values(event_guest) by email _time 
| where count >100
| `gsuite_suspicious_calendar_invite_filter`

Macros

The SPL above uses the following Macros:

:information_source: gsuite_suspicious_calendar_invite_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • _time
  • email
  • parameters.event_title
  • parameters.target_calendar_id
  • parameters.event_title

How To Implement

In order to successfully implement this search, you need to be ingesting logs related to gsuite (gsuite:calendar:json) having the file sharing metadata like file type, source owner, destination target user, description, etc. This search can also be made more specific by selecting specific emails, subdomains timeframe, organizational units, targeted user, etc. In order for the search to work for your environment please update yourdomain.com value in the query with the domain relavant for your organization.

Known False Positives

This search will also produce normal activity statistics. Fields such as email, ip address, name, parameters.organizer_calendar_id, parameters.target_calendar_id and parameters.event_title may give away phishing intent.For more specific results use email parameter.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
25.0 50 50 Gsuite suspicious calendar invite sent by $email$

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

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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