[New Rule] PowerShell Kerberos Ticket Request (#1715)

* PowerShell Kerberos Ticket Request Initial Rule

* bump date

rules/windows/credential_access_posh_request_ticket.toml

@@ -0,0 +1,76 @@
+[metadata]
+creation_date = "2021/01/24"
+maturity = "production"
+updated_date = "2021/01/24"
+
+[rule]
+author = ["Elastic"]
+description = """
+Detects PowerShell scripts that have the capability of requesting kerberos tickets, which is common step in
+Kerberoasting toolkits to crack service accounts.
+"""
+from = "now-9m"
+index = ["winlogbeat-*", "logs-windows.*"]
+language = "kuery"
+license = "Elastic License v2"
+name = "PowerShell Kerberos Ticket Request"
+references = [
+    "https://cobalt.io/blog/kerberoast-attack-techniques",
+    "https://github.com/EmpireProject/Empire/blob/master/data/module_source/credentials/Invoke-Kerberoast.ps1",
+]
+risk_score = 47
+rule_id = "eb610e70-f9e6-4949-82b9-f1c5bcd37c39"
+severity = "medium"
+tags = ["Elastic", "Host", "Windows", "Threat Detection", "Credential Access"]
+timestamp_override = "event.ingested"
+type = "query"
+
+query = '''
+event.category:process and 
+  powershell.file.script_block_text : (
+    KerberosRequestorSecurityToken
+  )
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+
+[[rule.threat.technique]]
+id = "T1003"
+name = "OS Credential Dumping"
+reference = "https://attack.mitre.org/techniques/T1003/"
+
+[[rule.threat.technique]]
+id = "T1558"
+name = "Steal or Forge Kerberos Tickets"
+reference = "https://attack.mitre.org/techniques/T1558/"
+
+    [[rule.threat.technique.subtechnique]]
+    id = "T1558.003"
+    name = "Kerberoasting"
+    reference = "https://attack.mitre.org/techniques/T1558/003/"
+
+[rule.threat.tactic]
+id = "TA0006"
+name = "Credential Access"
+reference = "https://attack.mitre.org/tactics/TA0006/"
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+
+[[rule.threat.technique]]
+id = "T1059"
+name = "Command and Scripting Interpreter"
+reference = "https://attack.mitre.org/techniques/T1059/"
+
+    [[rule.threat.technique.subtechnique]]
+    id = "T1059.001"
+    name = "PowerShell"
+    reference = "https://attack.mitre.org/techniques/T1059/001/"
+
+[rule.threat.tactic]
+id = "TA0002"
+name = "Execution"
+reference = "https://attack.mitre.org/tactics/TA0002/"