ID | Technique | Tactic |
---|---|---|
T1566.001 | Spearphishing Attachment | Initial Access |
T1566 | Phishing | Initial Access |
Detection: Gsuite Email Suspicious Subject With Attachment
Description
The following analytic identifies Gsuite emails with suspicious subjects and attachments commonly used in spear phishing attacks. It leverages Gsuite email logs, focusing on specific keywords in the subject line and known malicious file types in attachments. This activity is significant for a SOC as spear phishing is a prevalent method for initial compromise, often leading to further malicious actions. If confirmed malicious, this activity could result in unauthorized access, data exfiltration, or further malware deployment, posing a significant risk to the organization's security.
Search
1`gsuite_gmail` num_message_attachments > 0 subject IN ("*dhl*", "* ups *", "*delivery*", "*parcel*", "*label*", "*invoice*", "*postal*", "* fedex *", "* usps *", "* express *", "*shipment*", "*Banking/Tax*","*shipment*", "*new order*") attachment{}.file_extension_type IN ("doc", "docx", "xls", "xlsx", "ppt", "pptx", "pdf", "zip", "rar", "html","htm","hta")
2| rex field=source.from_header_address "[^@]+@(?<source_domain>[^@]+)"
3| rex field=destination{}.address "[^@]+@(?<dest_domain>[^@]+)"
4| where not source_domain="internal_test_email.com" and dest_domain="internal_test_email.com"
5| eval phase="plan"
6| eval severity="medium"
7| 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
8| `security_content_ctime(firstTime)`
9| `security_content_ctime(lastTime)`
10| `gsuite_email_suspicious_subject_with_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_subject_with_attachment_filter | search * |
gsuite_email_suspicious_subject_with_attachment_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
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
normal user or normal transaction may contain the subject and file type attachment that this detection try to search.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
Suspicious email from $source.address$ to $destination{}.address$ | 25 | 50 | 50 |
References
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