First time seen command line argument

SPLUNK detection rule by Bhavin Patel, Splunk · Apache-2.0

This search looks for command-line arguments that use a `/c` parameter to execute a command that has not previously been seen.

name: First time seen command line argument
id: a1b6e73f-98d5-470f-99ac-77aacd578473
version: 8
creation_date: '2020-04-29'
modification_date: '2026-05-13'
author: Bhavin Patel, Splunk
status: removed
type: Hunting
description: This search looks for command-line arguments that use a `/c` parameter to execute a command that has not previously been seen.
data_source:
    - Sysmon EventID 1
search: '| tstats `security_content_summariesonly` min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name = cmd.exe Processes.process = "* /c *" by Processes.process Processes.process_name Processes.parent_process_name Processes.dest| `drop_dm_object_name(Processes)`| `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | search [| tstats `security_content_summariesonly` earliest(_time) as firstTime latest(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process_name = cmd.exe Processes.process = "* /c *" by Processes.process | `drop_dm_object_name(Processes)` | inputlookup append=t previously_seen_cmd_line_arguments | stats min(firstTime) as firstTime, max(lastTime) as lastTime by process | outputlookup previously_seen_cmd_line_arguments | eval newCmdLineArgument=if(firstTime >= relative_time(now(), "-70m@m"), 1, 0) | where newCmdLineArgument=1 | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | table process] | `first_time_seen_command_line_argument_filter`'
how_to_implement: The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint` data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
known_false_positives: Legitimate programs can also use command-line arguments to execute. Please verify the command-line arguments to check what command/program is being executed. We recommend customizing the `first_time_seen_cmd_line_filter` macro to exclude legitimate parent_process_name
references: []
tags:
    analytic_story:
        - DHS Report TA18-074A
        - Suspicious Command-Line Executions
        - Orangeworm Attack Group
        - Possible Backdoor Activity Associated With MUDCARP Espionage Campaigns
        - Hidden Cobra Malware
    asset_type: Endpoint
    mitre_attack_id:
        - T1059.001
        - T1059.003
    product:
        - Splunk Enterprise
        - Splunk Enterprise Security
        - Splunk Cloud
    security_domain: endpoint
deprecation_info:
    reason: Detection deprecated as it no longer effectively identifies the intended malicious activity
    removed_in_version: 5.2.0
    replacement_content: []

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