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Description

Attackers often use spaces as a means to obfuscate an attachment's file extension. This search looks for messages with email attachments that have many spaces within the file names.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Email
  • Last Updated: 2017-09-19
  • Author: David Dorsey, Splunk
  • ID: 56e877a6-1455-4479-ada6-0550dc1e22f8

| tstats `security_content_summariesonly` count values(All_Email.recipient) as recipient_address min(_time) as firstTime max(_time) as lastTime from datamodel=Email where All_Email.file_name="*" by All_Email.src_user, All_Email.file_name All_Email.message_id 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `drop_dm_object_name("All_Email")` 
| eval space_ratio = (mvcount(split(file_name," "))-1)/len(file_name) 
| search space_ratio >= 0.1 
|  rex field=recipient_address "(?<recipient_user>.*)@" 
| `email_attachments_with_lots_of_spaces_filter`

Associated Analytic Story

How To Implement

You need to ingest data from emails. Specifically, the sender's address and the file names of any attachments must be mapped to the Email data model. The threshold ratio is set to 10%, but this value can be configured to suit each environment.
Splunk Phantom Playbook Integration
If Splunk Phantom is also configured in your environment, a playbook called "Suspicious Email Attachment Investigate and Delete" can be configured to run when any results are found by this detection search. To use this integration, install the Phantom App for Splunk https://splunkbase.splunk.com/app/3411/ and add the correct hostname to the "Phantom Instance" field in the Adaptive Response Actions when configuring this detection search. The notable event will be sent to Phantom and the playbook will gather further information about the file attachment and its network behaviors. If Phantom finds malicious behavior and an analyst approves of the results, the email will be deleted from the user's inbox.

Required field

  • _time
  • All_Email.recipient
  • All_Email.file_name
  • All_Email.src_user
  • All_Email.file_name
  • All_Email.message_id

Kill Chain Phase

  • Delivery

Known False Positives

None at this time

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

source | version: 2