PowerShell Downgrade Attack - PowerShell

Status: test
Severity: medium
Log source: category ps_classic_start, product windows
Author: Florian Roth (Nextron Systems), Lee Holmes (idea), Harish Segar (improvements)
Source: github.com/SigmaHQ/sigma

Detects PowerShell downgrade attack by comparing the host versions with the actually used engine version 2.0

MITRE ATT&CK coverage

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

Telemetry coverage

Provider	Record / event type
PowerShell	Event ID 400

Rule body

title: PowerShell Downgrade Attack - PowerShell
id: 6331d09b-4785-4c13-980f-f96661356249
status: test
description: Detects PowerShell downgrade attack by comparing the host versions with the actually used engine version 2.0
references:
    - http://www.leeholmes.com/blog/2017/03/17/detecting-and-preventing-powershell-downgrade-attacks/
author: Florian Roth (Nextron Systems), Lee Holmes (idea), Harish Segar (improvements)
date: 2017-03-22
modified: 2023-10-27
tags:
    - attack.execution
    - attack.t1059.001
logsource:
    product: windows
    category: ps_classic_start
detection:
    selection:
        Data|contains: 'EngineVersion=2.'
    filter_main:
        Data|contains: 'HostVersion=2.'
    condition: selection and not filter_main
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not filter_main

Stage 1: `selection`

selection:
    Data|contains: 'EngineVersion=2.'

Stage 2: `not filter_main`

filter_main:
    Data|contains: 'HostVersion=2.'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Data`	match	`HostVersion=2.`	`excludes:Data` `field:"Data" value:"HostVersion=2."`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Data`	match	`EngineVersion=2.` corpus 2 (sigma 2)	`field:"Data" kind:match value:"EngineVersion=2."`