Detection rules › Sigma

PowerShell Module File Created By Non-PowerShell Process

Severity
medium
Author
Nasreddine Bencherchali (Nextron Systems)
Source
upstream

Detects the creation of a new PowerShell module ".psm1", ".psd1", ".dll", ".ps1", etc. by a non-PowerShell process

Event coverage

ProviderEvent IDTitle
Sysmon11FileCreate

Stages and Predicates

Stage 1: selection

or:
TargetFilename|contains: '\PowerShell\7\Modules\'
TargetFilename|contains: '\WindowsPowerShell\Modules\'

Stage 2: not 1 of filter_main_*

or:
Image|endswith: ':\Program Files\PowerShell\7-preview\pwsh.exe'
Image|endswith: ':\Program Files\PowerShell\7\pwsh.exe'
Image|endswith: ':\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell.exe'
Image|endswith: ':\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell_ise.exe'
Image|endswith: ':\Windows\SysWOW64\poqexec.exe'
Image|endswith: ':\Windows\System32\WindowsPowerShell\v1.0\powershell.exe'
Image|endswith: ':\Windows\System32\WindowsPowerShell\v1.0\powershell_ise.exe'
Image|endswith: ':\Windows\System32\poqexec.exe'
Image: 'C:\Windows\SysWOW64\msiexec.exe'
Image: 'C:\Windows\System32\msiexec.exe'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
Imageends_with
  • :\Program Files\PowerShell\7-preview\pwsh.exe
  • :\Program Files\PowerShell\7\pwsh.exe
  • :\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell.exe
  • :\Windows\SysWOW64\WindowsPowerShell\v1.0\powershell_ise.exe
  • :\Windows\SysWOW64\poqexec.exe
  • :\Windows\System32\WindowsPowerShell\v1.0\powershell.exe
  • :\Windows\System32\WindowsPowerShell\v1.0\powershell_ise.exe
  • :\Windows\System32\poqexec.exe
Imageeq
  • C:\Windows\SysWOW64\msiexec.exe corpus 4 (sigma 4)
  • C:\Windows\System32\msiexec.exe corpus 4 (sigma 4)
TargetFilenamematch
  • \PowerShell\7\Modules\ corpus 2 (sigma 2)
  • \WindowsPowerShell\Modules\ corpus 3 (sigma 3)

Neighbors

Stricter alternatives (narrower than this rule)

The rules below may be useful if you find the current rule is too noisy / lacks specificity.