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_script_executing_powershell.toml

@@ -0,0 +1,40 @@
+[metadata]
+creation_date = "2020/02/18"
+ecs_version = ["1.4.0"]
+maturity = "production"
+updated_date = "2020/02/18"
+
+[rule]
+author = ["Elastic"]
+description = """
+Identifies a PowerShell process launched by either cscript.exe or wscript.exe. Observing Windows scripting processes
+executing a PowerShell script, may be indicative of malicious activity.
+"""
+index = ["winlogbeat-*"]
+language = "kuery"
+license = "Elastic License"
+name = "Windows Script Executing PowerShell"
+risk_score = 21
+rule_id = "f545ff26-3c94-4fd0-bd33-3c7f95a3a0fc"
+severity = "low"
+tags = ["Elastic", "Windows"]
+type = "query"
+
+query = '''
+event.action:"Process Create (rule: ProcessCreate)" and process.parent.name:(cscript.exe or wscript.exe) and process.name:powershell.exe
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+id = "T1193"
+name = "Spearphishing Attachment"
+reference = "https://attack.mitre.org/techniques/T1193/"
+
+
+[rule.threat.tactic]
+id = "TA0002"
+name = "Execution"
+reference = "https://attack.mitre.org/tactics/TA0002/"
+