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Description

This search uses the Machine Learning Toolkit (MLTK) to identify spikes in the number of Server Message Block (SMB) connections.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Network_Traffic
  • Last Updated: 2020-07-22
  • Author: Rico Valdez, Splunk
  • ID: d25773ba-9ad8-48d1-858e-07ad0bbeb828

ATT&CK

ID Technique Tactic
T1021.002 SMB/Windows Admin Shares Lateral Movement

| tstats `security_content_summariesonly` count values(All_Traffic.dest_ip) as dest values(All_Traffic.dest_port) as port from datamodel=Network_Traffic where All_Traffic.dest_port=139 OR All_Traffic.dest_port=445 OR All_Traffic.app=smb by _time span=1h, All_Traffic.src 
| eval HourOfDay=strftime(_time, "%H") 
| eval DayOfWeek=strftime(_time, "%A") 
| `drop_dm_object_name(All_Traffic)` 
| apply smb_pdfmodel threshold=0.001 
| rename "IsOutlier(count)" as isOutlier 
| search isOutlier > 0 
| sort -count 
| table _time src dest port count 
| `smb_traffic_spike___mltk_filter` 

Associated Analytic Story

How To Implement

To successfully implement this search, you will need to ensure that DNS data is populating the Network_Resolution data model. In addition, the Machine Learning Toolkit (MLTK) version 4.2 or greater must be installed on your search heads, along with any required dependencies. Finally, the support search "Baseline of SMB Traffic - MLTK" must be executed before this detection search, because it builds a machine-learning (ML) model over the historical data used by this search. It is important that this search is run in the same app context as the associated support search, so that the model created by the support search is available for use. You should periodically re-run the support search to rebuild the model with the latest data available in your environment.
This search produces a field (Number of events,count) that are not yet supported by ES Incident Review and therefore cannot be viewed when a notable event is raised. This field contributes additional context to the notable. To see the additional metadata, add the following field, if not already present, to Incident Review - Event Attributes (Configure > Incident Management > Incident Review Settings > Add New Entry): \

  1. Label: Number of events, Field: count
    Detailed documentation on how to create a new field within Incident Review is found here: https://docs.splunk.com/Documentation/ES/5.3.0/Admin/Customizenotables#Add_a_field_to_the_notable_event_details

Required field

  • _time
  • All_Traffic.dest_ip
  • All_Traffic.dest_port
  • All_Traffic.app
  • All_Traffic.src

Kill Chain Phase

  • Actions on Objectives

Known False Positives

If you are seeing more results than desired, you may consider reducing the value of the threshold in the search. You should also periodically re-run the support search to re-build the ML model on the latest data. Please update the smb_traffic_spike_mltk_filter macro to filter out false positive results

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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