Populate rules/ directory.

Co-Authored-By: Brent Murphy <56412096+bm11100@users.noreply.github.com>
Co-Authored-By: Craig Chamberlain <randomuserid@users.noreply.github.com>
Co-Authored-By: David French <56409778+threat-punter@users.noreply.github.com>
Co-Authored-By: Derek Ditch <dcode@users.noreply.github.com>
Co-Authored-By: Justin Ibarra <brokensound77@users.noreply.github.com>

rules/windows/execution_command_shell_started_by_powershell.toml

@@ -0,0 +1,49 @@
+[metadata]
+creation_date = "2020/02/18"
+ecs_version = ["1.4.0"]
+maturity = "production"
+updated_date = "2020/02/18"
+
+[rule]
+author = ["Elastic"]
+description = "Identifies a suspicious parent child process relationship with cmd.exe descending from PowerShell.exe."
+index = ["winlogbeat-*"]
+language = "kuery"
+license = "Elastic License"
+name = "PowerShell spawning Cmd"
+risk_score = 21
+rule_id = "0f616aee-8161-4120-857e-742366f5eeb3"
+severity = "low"
+tags = ["Elastic", "Windows"]
+type = "query"
+
+query = '''
+process.parent.name:powershell.exe and process.name:cmd.exe
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1059"
+name = "Command-Line Interface"
+reference = "https://attack.mitre.org/techniques/T1059/"
+
+
+[rule.threat.tactic]
+id = "TA0002"
+name = "Execution"
+reference = "https://attack.mitre.org/tactics/TA0002/"
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1086"
+name = "PowerShell"
+reference = "https://attack.mitre.org/techniques/T1086/"
+
+
+[rule.threat.tactic]
+id = "TA0002"
+name = "Execution"
+reference = "https://attack.mitre.org/tactics/TA0002/"
+