Change PowerShell Policies to an Insecure Level

Severity: medium
Author: frack113
Source: upstream

Detects changing the PowerShell script execution policy to a potentially insecure level using the "-ExecutionPolicy" flag.

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\powershell.exe'
Image|endswith: '\powershell_ise.exe'
Image|endswith: '\pwsh.exe'
OriginalFileName: PowerShell.EXE
OriginalFileName: powershell_ise.exe
OriginalFileName: pwsh.dll

Stage 2: `all of selection_option`

or:
CommandLine|contains: ' -ep '
CommandLine|contains: ' -exec '
CommandLine|contains: '-executionpolicy '

Stage 3: `all of selection_level`

or:
CommandLine|contains: Bypass
CommandLine|contains: Unrestricted

Stage 4: `not 1 of filter_main_powershell_core`

or:
CommandLine|contains: '-NoProfile -ExecutionPolicy Bypass -File "C:\Program Files (x86)\PowerShell\7\'
CommandLine|contains: '-NoProfile -ExecutionPolicy Bypass -File "C:\Program Files\PowerShell\7\'
ParentImage: ['C:\Windows\SysWOW64\msiexec.exe', 'C:\Windows\System32\msiexec.exe']

Stage 5: `not 1 of filter_optional_avast`

or:
CommandLine|contains: '-ExecutionPolicy ByPass -File "C:\Program Files (x86)\Avast Software\Avast\'
CommandLine|contains: '-ExecutionPolicy ByPass -File "C:\Program Files\Avast Software\Avast'
or:
ParentImage|contains: 'C:\Program Files (x86)\Avast Software\Avast\'
ParentImage|contains: 'C:\Program Files\Avast Software\Avast\'
ParentImage|contains: '\instup.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.

Field	Kind	Values
`CommandLine`	match	`-ep` `-exec` `-ExecutionPolicy ByPass -File "C:\Program Files (x86)\Avast Software\Avast\` `-ExecutionPolicy ByPass -File "C:\Program Files\Avast Software\Avast` `-NoProfile -ExecutionPolicy Bypass -File "C:\Program Files (x86)\PowerShell\7\` `-NoProfile -ExecutionPolicy Bypass -File "C:\Program Files\PowerShell\7\` `-executionpolicy` `Bypass` corpus 2 (sigma 2) `Unrestricted` corpus 2 (sigma 2)
`Image`	ends_with	`\powershell.exe` corpus 143 (sigma 143) `\powershell_ise.exe` corpus 27 (sigma 27) `\pwsh.exe` corpus 140 (sigma 140)
`OriginalFileName`	eq	`PowerShell.EXE` corpus 64 (sigma 60, splunk 4) `powershell_ise.exe` corpus 6 (sigma 6) `pwsh.dll` corpus 72 (sigma 68, splunk 4)
`ParentImage`	eq	`C:\Windows\SysWOW64\msiexec.exe` corpus 2 (sigma 2) `C:\Windows\System32\msiexec.exe` corpus 3 (sigma 3)
`ParentImage`	match	`C:\Program Files (x86)\Avast Software\Avast\` `C:\Program Files\Avast Software\Avast\` `\instup.exe`

Change PowerShell Policies to an Insecure Level

MITRE ATT&CK coverage

Event coverage

Stages and Predicates

Stage 1: all of selection_img

Stage 2: all of selection_option

Stage 3: all of selection_level