Add: sigma rules (#175)

rules/sigma/windows/powershell/powershell_script/powershell_timestomp.yml

@@ -0,0 +1,35 @@
+
+title: Powershell Timestomp
+author: frack113
+date: 2021/08/03
+description: Adversaries may modify file time attributes to hide new or changes to
+  existing files. Timestomping is a technique that modifies the timestamps of a file
+  (the modify, access, create, and change times), often to mimic files that are in
+  the same folder.
+detection:
+  SELECTION_1:
+    EventID: 4104
+  SELECTION_2:
+    ScriptBlockText:
+    - '*.CreationTime =*'
+    - '*.LastWriteTime =*'
+    - '*.LastAccessTime =*'
+    - '*[IO.File]::SetCreationTime*'
+    - '*[IO.File]::SetLastAccessTime*'
+    - '*[IO.File]::SetLastWriteTime*'
+  condition: (SELECTION_1 and SELECTION_2)
+falsepositives:
+- legitime admin script
+id: c6438007-e081-42ce-9483-b067fbef33c3
+level: medium
+logsource:
+  definition: EnableScriptBlockLogging must be set to enable
+  product: windows
+  service: powershell
+references:
+- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1070.006/T1070.006.md
+- https://www.offensive-security.com/metasploit-unleashed/timestomp/
+status: experimental
+tags:
+- attack.defense_evasion
+- attack.t1070.006