Sample rules
Gsuite Email Suspicious Subject With Attachment
- source: splunk
- technicques:
- T1566.001
- T1566
Description
This search is to detect a gsuite email contains suspicious subject having known file type used in spear phishing. This technique is a common and effective entry vector of attacker to compromise a network by luring the user to click or execute the suspicious attachment send from external email account because of the effective social engineering of subject related to delivery, bank and so on. On the other hand this detection may catch a normal email traffic related to legitimate transaction so better to check the email sender, spelling and etc. avoid click link or opening the attachment if you are not expecting this type of e-mail.
Detection logic
`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")
| rex field=source.from_header_address "[^@]+@(?<source_domain>[^@]+)"
| rex field=destination{}.address "[^@]+@(?<dest_domain>[^@]+)"
| where not source_domain="internal_test_email.com" and dest_domain="internal_test_email.com"
| 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_subject_with_attachment_filter`
Gsuite Suspicious Shared File Name
- source: splunk
- technicques:
- T1566.001
- T1566
Description
This search is to detect a shared file in google drive with suspicious file name that are commonly used by spear phishing campaign. This technique is very popular to lure the user by running a malicious document or click a malicious link within the shared file that will redirected to malicious website. This detection can also catch some normal email communication between organization and its external customer.
Detection logic
`gsuite_drive` parameters.owner_is_team_drive=false "parameters.doc_title" IN ("*dhl*", "* ups *", "*delivery*", "*parcel*", "*label*", "*invoice*", "*postal*", "*fedex*", "* usps *", "* express *", "*shipment*", "*Banking/Tax*","*shipment*", "*new order*") parameters.doc_type IN ("document","pdf", "msexcel", "msword", "spreadsheet", "presentation")
| rex field=parameters.owner "[^@]+@(?<source_domain>[^@]+)"
| rex field=parameters.target_user "[^@]+@(?<dest_domain>[^@]+)"
| where not source_domain="internal_test_email.com" and dest_domain="internal_test_email.com"
| eval phase="plan"
| eval severity="low"
| stats count min(_time) as firstTime max(_time) as lastTime by email parameters.owner parameters.target_user parameters.doc_title parameters.doc_type phase severity
| rename parameters.target_user AS user
| `security_content_ctime(firstTime)`
| `security_content_ctime(lastTime)`
| `gsuite_suspicious_shared_file_name_filter`