[New Rule] Suspicious Execution from a Mounted Device (#1230)

* Create defense_evasion_suspicious_execution_from_mounted_device.toml
Co-authored-by: Justin Ibarra <brokensound77@users.noreply.github.com>

rules/windows/defense_evasion_suspicious_execution_from_mounted_device.toml

@@ -0,0 +1,80 @@
+[metadata]
+creation_date = "2021/05/28"
+maturity = "production"
+updated_date = "2021/05/28"
+
+[rule]
+author = ["Elastic"]
+description = """
+Identifies when a script interpreter or signed binary is launched via a non-standard working directory. An attacker may
+use this technique to evade defenses.
+"""
+from = "now-9m"
+index = ["winlogbeat-*", "logs-endpoint.events.*", "logs-windows.*"]
+language = "eql"
+license = "Elastic License v2"
+name = "Suspicious Execution from a Mounted Device"
+references = [
+    "https://www.microsoft.com/security/blog/2021/05/27/new-sophisticated-email-based-attack-from-nobelium/",
+    "https://www.volexity.com/blog/2021/05/27/suspected-apt29-operation-launches-election-fraud-themed-phishing-campaigns/",
+]
+risk_score = 47
+rule_id = "8a1d4831-3ce6-4859-9891-28931fa6101d"
+severity = "medium"
+tags = ["Elastic", "Host", "Windows", "Threat Detection", "Defense Evasion"]
+timestamp_override = "event.ingested"
+type = "eql"
+
+query = '''
+process where event.type == "start" and process.executable : "C:\\*" and
+  (process.working_directory : "?:\\" and not process.working_directory: "C:\\") and
+  process.parent.name : "explorer.exe" and
+  process.name : ("rundll32.exe", "mshta.exe", "powershell.exe", "pwsh.exe", "cmd.exe", "regsvr32.exe",
+                  "cscript.exe", "wscript.exe")
+'''
+
+
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+reference = "https://attack.mitre.org/techniques/T1218/"
+id = "T1218"
+name = "Signed Binary Proxy Execution"
+[[rule.threat.technique.subtechnique]]
+reference = "https://attack.mitre.org/techniques/T1218/011/"
+id = "T1218.011"
+name = "Rundll32"
+
+[[rule.threat.technique.subtechnique]]
+reference = "https://attack.mitre.org/techniques/T1218/005/"
+id = "T1218.005"
+name = "Mshta"
+
+[[rule.threat.technique.subtechnique]]
+reference = "https://attack.mitre.org/techniques/T1218/010/"
+id = "T1218.010"
+name = "Regsvr32"
+
+
+
+[rule.threat.tactic]
+reference = "https://attack.mitre.org/tactics/TA0005/"
+id = "TA0005"
+name = "Defense Evasion"
+[[rule.threat]]
+framework = "MITRE ATT&CK"
+[[rule.threat.technique]]
+reference = "https://attack.mitre.org/techniques/T1059/"
+id = "T1059"
+name = "Command and Scripting Interpreter"
+[[rule.threat.technique.subtechnique]]
+reference = "https://attack.mitre.org/techniques/T1059/001/"
+id = "T1059.001"
+name = "PowerShell"
+
+
+
+[rule.threat.tactic]
+reference = "https://attack.mitre.org/tactics/TA0002/"
+id = "TA0002"
+name = "Execution"