SMB Traffic Spike

SPLUNK detection rule by David Dorsey, Splunk · Apache-2.0

The following analytic detects spikes in Server Message Block (SMB) traffic connections, which are used for sharing files and resources between computers. It leverages network traffic logs to monitor connections on ports 139 and 445, and SMB application usage. By calculating the average and standard deviation of SMB connections over the past 70 minutes, it identifies sources exceeding two standard deviations from the average. This activity is significant as it may indicate potential SMB-based attacks, such as ransomware or data theft. If confirmed malicious, attackers could exfiltrate data or spread malware within the network.

name: SMB Traffic Spike
id: 7f5fb3e1-4209-4914-90db-0ec21b936378
version: 11
creation_date: '2019-10-16'
modification_date: '2026-05-13'
author: David Dorsey, Splunk
status: experimental
type: Anomaly
description: The following analytic detects spikes in Server Message Block (SMB) traffic connections, which are used for sharing files and resources between computers. It leverages network traffic logs to monitor connections on ports 139 and 445, and SMB application usage. By calculating the average and standard deviation of SMB connections over the past 70 minutes, it identifies sources exceeding two standard deviations from the average. This activity is significant as it may indicate potential SMB-based attacks, such as ransomware or data theft. If confirmed malicious, attackers could exfiltrate data or spread malware within the network.
data_source: []
search: |-
    | tstats `security_content_summariesonly` count 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
    | `drop_dm_object_name("All_Traffic")`
    | eventstats max(_time) as maxtime
    | stats count as num_data_samples max(eval(if(_time >= relative_time(maxtime, "-70m@m"), count, null))) as count avg(eval(if(_time<relative_time(maxtime, "-70m@m"), count, null))) as avg stdev(eval(if(_time<relative_time(maxtime, "-70m@m"), count, null))) as stdev
      BY src
    | eval upperBound=(avg+stdev*2), isOutlier=if(count > upperBound AND num_data_samples >=50, 1, 0)
    | where isOutlier=1
    | table src count
    | `smb_traffic_spike_filter`
how_to_implement: This search requires you to be ingesting your network traffic logs and populating the `Network_Traffic` data model.
known_false_positives: A file server may experience high-demand loads that could cause this analytic to trigger.
references: []
intermediate_findings:
    entities:
        - field: src
          type: system
          score: 20
          message: Anomalous splike of SMB traffic sent from $src$
analytic_story:
    - Emotet Malware DHS Report TA18-201A
    - Hidden Cobra Malware
    - Ransomware
    - DHS Report TA18-074A
asset_type: Endpoint
mitre_attack_id:
    - T1021.002
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: network
security_domain: network

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69380d09-1c57-4fc3-ba38-1964d8baed57

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