From c8a376179b1732043250d69eabc369eb7db204a2 Mon Sep 17 00:00:00 2001
From: Fukusuke Takahashi <41001169+fukusuket@users.noreply.github.com>
Date: Sun, 11 Aug 2024 18:54:46 +0900
Subject: [PATCH] Merge PR #4964 from @fukusuket - Fix rules to not use
 `Lookahead` regex

fix: Powershell Token Obfuscation - Powershell - Changed to not use Lookahead regex
fix: Powershell Token Obfuscation - Process Creation - Changed to not use Lookahead regex

---------

Co-authored-by: nasbench <8741929+nasbench@users.noreply.github.com>
---
 .../powershell_script/posh_ps_token_obfuscation.yml    |  8 +++++---
 .../proc_creation_win_powershell_token_obfuscation.yml | 10 ++++++----
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/rules/windows/powershell/powershell_script/posh_ps_token_obfuscation.yml b/rules/windows/powershell/powershell_script/posh_ps_token_obfuscation.yml
index 507343c29..fe4cc6b83 100644
--- a/rules/windows/powershell/powershell_script/posh_ps_token_obfuscation.yml
+++ b/rules/windows/powershell/powershell_script/posh_ps_token_obfuscation.yml
@@ -9,7 +9,7 @@ references:
     - https://github.com/danielbohannon/Invoke-Obfuscation
 author: frack113
 date: 2022/12/27
-modified: 2024/08/10
+modified: 2024/08/11
 tags:
     - attack.defense_evasion
     - attack.t1027.009
@@ -23,11 +23,13 @@ detection:
         #   IN`V`o`Ke-eXp`ResSIOn (Ne`W-ob`ject Net.WebClient).DownloadString
         #   &('In'+'voke-Expressi'+'o'+'n') (.('New-Ob'+'jec'+'t') Net.WebClient).DownloadString
         #   &("{2}{3}{0}{4}{1}"-f 'e','Expression','I','nvok','-') (&("{0}{1}{2}"-f'N','ew-O','bject') Net.WebClient).DownloadString
-        #   ${e`Nv:pATh}
         - ScriptBlockText|re: '\w+`(\w+|-|.)`[\w+|\s]'
         # - ScriptBlockText|re: '\((\'(\w|-|\.)+\'\+)+\'(\w|-|\.)+\'\)' TODO: fixme
         - ScriptBlockText|re: '"(\{\d\}){2,}"\s*-f'  # trigger on at least two placeholders. One might be used for legitimate string formatting
-        - ScriptBlockText|re: '(?i)\$\{(?=.*`)+?`?e`?n`?v`?:`?p`?a`?t`?h`?\}'
+        #   ${e`Nv:pATh}
+        - ScriptBlockText|re: '(?i)\$\{`?e`?n`?v`?:`?p`?a`?t`?h`?\}'
+    filter_envpath:
+        ScriptBlockText|contains: '${env:path}' # TODO: Fix this. See https://github.com/SigmaHQ/sigma/pull/4964
     filter_chocolatey:
         ScriptBlockText|contains:
             - 'it will return true or false instead'  # Chocolatey install script https://github.com/chocolatey/chocolatey
diff --git a/rules/windows/process_creation/proc_creation_win_powershell_token_obfuscation.yml b/rules/windows/process_creation/proc_creation_win_powershell_token_obfuscation.yml
index f7be94afa..6c88f8b51 100644
--- a/rules/windows/process_creation/proc_creation_win_powershell_token_obfuscation.yml
+++ b/rules/windows/process_creation/proc_creation_win_powershell_token_obfuscation.yml
@@ -9,7 +9,7 @@ references:
     - https://github.com/danielbohannon/Invoke-Obfuscation
 author: frack113
 date: 2022/12/27
-modified: 2024/08/09
+modified: 2024/08/11
 tags:
     - attack.defense_evasion
     - attack.t1027.009
@@ -22,12 +22,14 @@ detection:
         #   IN`V`o`Ke-eXp`ResSIOn (Ne`W-ob`ject Net.WebClient).DownloadString
         #   &('In'+'voke-Expressi'+'o'+'n') (.('New-Ob'+'jec'+'t') Net.WebClient).DownloadString
         #   &("{2}{3}{0}{4}{1}"-f 'e','Expression','I','nvok','-') (&("{0}{1}{2}"-f'N','ew-O','bject') Net.WebClient).DownloadString
-        #   ${e`Nv:pATh}
         - CommandLine|re: '\w+`(\w+|-|.)`[\w+|\s]'
         # - CommandLine|re: '\((\'(\w|-|\.)+\'\+)+\'(\w|-|\.)+\'\)' TODO: fixme
         - CommandLine|re: '"(\{\d\})+"\s*-f'
-        - CommandLine|re: '(?i)\$\{(?=.*`)+?`?e`?n`?v`?:`?p`?a`?t`?h`?\}'
-    condition: selection
+        #   ${e`Nv:pATh}
+        - CommandLine|re: '(?i)\$\{`?e`?n`?v`?:`?p`?a`?t`?h`?\}'
+    filter_main_envpath:
+        CommandLine|contains: '${env:path}'
+    condition: selection and not 1 of filter_main_*
 falsepositives:
     - Unknown
 level: high