:warning: THIS IS A EXPERIMENTAL DETECTION

This detection has been marked experimental by the Splunk Threat Research team. This means we have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.

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Description

This search looks for command-line arguments that use a /c parameter to execute a command that has not previously been seen. This is an implementation on SPL2 of the rule First time seen command line argument by @bpatel. 'The following analytic identifies first time seen command-line arguments on a single endpoint. The analytic looks for arguments instantiated by cmd.exe /c and the associated command-line. Adversaries automate or spawn multiple processes using this method, this analytic may assist with identifying the first time it's been found on this endpoint.'

  • Type: Anomaly
  • Product: Splunk Behavioral Analytics
  • Datamodel: Endpoint_Processes
  • Last Updated: 2021-11-30
  • Author: Ignacio Bermudez Corrales, Splunk
  • ID: fc0edc95-ff2b-48b0-9f6f-63da3789fd23

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1059 Command and Scripting Interpreter Execution
T1202 Indirect Command Execution Defense Evasion
Kill Chain Phase
  • Command & Control
  • Actions on Objectives
NIST
  • PR.PT
  • DE.CM
  • PR.IP
CIS20
  • CIS 3
  • CIS 8
CVE
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| from read_ssa_enriched_events() 
| eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)) 
| eval dest_user_id=ucast(map_get(input_event, "dest_user_id"), "string", null), dest_device_id=ucast(map_get(input_event, "dest_device_id"), "string", null), process_name=ucast(map_get(input_event, "process_name"), "string", null), cmd_line=ucast(map_get(input_event, "process"), "string", null), cmd_line_norm=lower(cmd_line), cmd_line_norm=replace(cmd_line_norm, /[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}/, "GUID"), cmd_line_norm=replace(cmd_line_norm, /(?<=\s)+\\[^:]*(?=\\.*\.\w{3}(\s
|$)+)/, "\\PATH"), /* replaces " \\Something\\Something\\command.ext" => "PATH\\command.ext" */ cmd_line_norm=replace(cmd_line_norm, /\w:\\[^:]*(?=\\.*\.\w{3}(\s
|$)+)/, "\\PATH"), /* replaces "C:\\Something\\Something\\command.ext" => "PATH\\command.ext" */ cmd_line_norm=replace(cmd_line_norm, /\d+/, "N"), event_id=ucast(map_get(input_event, "event_id"), "string", null) 
| where process_name="cmd.exe" AND match_regex(ucast(cmd_line, "string", ""), /.* \/[cC] .*/)=true 
| select process_name, cmd_line, cmd_line_norm, timestamp, dest_device_id, dest_user_id 
| first_time_event input_columns=["cmd_line_norm"] 
| where first_time_cmd_line_norm 
| eval start_time = timestamp, end_time = timestamp, entities = mvappend(dest_device_id, dest_user_id), body=create_map(["event_id", event_id, "cmd_line", cmd_line, "process_name", process_name]) 
| into write_ssa_detected_events();

Macros

The SPL above uses the following Macros:

:information_source: first_time_seen_command_line_argument_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

  • process_name
  • _time
  • dest_device_id
  • dest_user_id
  • process
  • cmd_line

How To Implement

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

Legitimate programs use command-line arguments to execute. Verify the command-line arguments to check what command/program is being executed. Filtering will be needed.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
30.0 50 60 A process $process_name$ ha been identified in the environment with a command-line $cmd_line$ not previously seen before on host $dest_device_id$

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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: 4