Rule: Detect base64 encoded PowerShell shellcode

https://twitter.com/cyb3rops/status/1063072865992523776

rules/windows/builtin/win_powershell_b64_shellcode.yml

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+action: global
+title: PowerShell Base64 Encoded Shellcode
+description: Detects Base64 encoded Shellcode 
+status: experimental
+references:
+    - https://twitter.com/cyb3rops/status/1063072865992523776
+author: Florian Roth
+date: 2018/11/17
+tags:
+    - attack.defense_evasion
+    - attack.t1036
+detection:
+    condition: selection1 and selection2
+falsepositives: 
+    - Unknown
+level: critical
+---
+# Windows Audit Log
+logsource:
+    product: windows
+    service: security
+    description: 'Requirements: Audit Policy : Detailed Tracking > Audit Process creation, Group Policy : Administrative Templates\System\Audit Process Creation'
+detection:
+    selection1:
+        EventID: 4688
+        ProcesssCommandLine: '*AAAAYInlM*'
+    selection2:
+        ProcesssCommandLine: 
+            - '*OiCAAAAYInlM*'
+            - '*OiJAAAAYInlM*'
+---
+# Sysmon
+logsource:
+    product: windows
+    service: sysmon
+detection:
+    selection1:
+        EventID: 1
+        CommandLine: '*AAAAYInlM*'
+    selection2:
+        CommandLine: 
+            - '*OiCAAAAYInlM*'
+            - '*OiJAAAAYInlM*'
+

rules/windows/powershell/powershell_shellcode_b64.yml

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+title: PowerShell ShellCode
+status: experimental
+description: Detects Base64 encoded Shellcode
+references:
+    - https://twitter.com/cyb3rops/status/1063072865992523776
+tags:
+    - attack.execution
+author: David Ledbetter (shellcode), Florian Roth (rule)
+date: 2018/11/17
+logsource:
+    product: windows
+    service: powershell
+    description: 'Script block logging must be enabled'
+detection:
+    selection:
+        EventID: 4104
+    keyword1: 
+        - '*AAAAYInlM*'
+    keyword2: 
+        - '*OiCAAAAYInlM*'
+        - '*OiJAAAAYInlM*'
+    condition: selection and keyword1 and keyword2
+falsepositives:
+    - Unknown
+level: critical