Whoami Execution

Severity: info
Type: hunt
Author: Google Cloud Security
Source: github.com/chronicle/detection-rules

Detects the execution of whoami, which is often used by attackers after exploitation to establish what credentials they are logged in under

MITRE ATT&CK coverage

Tactic	Techniques
Discovery	`T1033` System Owner/User Discovery

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

// Copyright 2023 Google LLC. Licensed under Apache-2.0.

rule whoami_execution {

  meta:
    author = "Google Cloud Security"
    description = "Detects the execution of whoami, which is often used by attackers after exploitation to establish what credentials they are logged in under"
    rule_id = "mr_4372a068-1411-449f-b572-dc2b9358b5f4"
    rule_name = "Whoami Execution"
    type = "hunt"
    data_source = "microsoft sysmon, microsoft windows events"
    tactic = "TA0007"
    technique = "T1033"
    platform = "Windows"
    severity = "Info"
    priority = "Info"

  events:
    $process.metadata.event_type = "PROCESS_LAUNCH"
    $process.target.process.command_line = "whoami"

  outcome:
    $risk_score = 10
    // added to populate alert graph with additional context
    $principal_hostname = $process.principal.hostname
    $principal_process_pid = $process.principal.process.pid
    $principal_process_command_line = $process.principal.process.command_line
    $principal_process_file_sha256 = $process.principal.process.file.sha256
    $principal_process_file_full_path = $process.principal.process.file.full_path
    $principal_process_product_specific_process_id = $process.principal.process.product_specific_process_id
    $principal_process_parent_process_product_specific_process_id = $process.principal.process.parent_process.product_specific_process_id
    $target_process_pid = $process.target.process.pid
    $target_process_command_line = $process.target.process.command_line
    $target_process_file_sha256 = $process.target.process.file.sha256
    $target_process_file_full_path = $process.target.process.file.full_path
    $target_process_product_specific_process_id = $process.target.process.product_specific_process_id
    $principal_user_userid = $process.principal.user.userid

  condition:
    $process
}

YARA-L rule structure

Condition

Fires when at least one $process event.

Events

`$process` `PROCESS_LAUNCH` (`1`, `4688`)

target.process.command_line = "whoami"

Outcome

Outcome variables add context to a detection. When the rule generates an alert, $risk_score is displayed with it.

Field	Expression
`risk_score`	`10`
`principal_hostname`	`$process.principal.hostname`
`principal_process_pid`	`$process.principal.process.pid`
`principal_process_command_line`	`$process.principal.process.command_line`
`principal_process_file_sha256`	`$process.principal.process.file.sha256`
`principal_process_file_full_path`	`$process.principal.process.file.full_path`
`principal_process_product_specific_process_id`	`$process.principal.process.product_specific_process_id`
`principal_process_parent_process_product_specific_process_id`	`$process.principal.process.parent_process.product_specific_process_id`
`target_process_pid`	`$process.target.process.pid`
`target_process_command_line`	`$process.target.process.command_line`
`target_process_file_sha256`	`$process.target.process.file.sha256`
`target_process_file_full_path`	`$process.target.process.file.full_path`
`target_process_product_specific_process_id`	`$process.target.process.product_specific_process_id`
`principal_user_userid`	`$process.principal.user.userid`