Suspicious PowerShell IEX Execution Patterns

SIGMA detection rule by Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems) · NOASSERTION

Detects suspicious ways to run Invoke-Execution using IEX alias

title: Suspicious PowerShell IEX Execution Patterns
id: 09576804-7a05-458e-a817-eb718ca91f54
status: test
description: Detects suspicious ways to run Invoke-Execution using IEX alias
references:
    - https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/invoke-expression?view=powershell-7.2
    - https://www.huntress.com/blog/slashandgrab-screen-connect-post-exploitation-in-the-wild-cve-2024-1709-cve-2024-1708
author: Florian Roth (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2022-03-24
modified: 2022-11-28
tags:
    - attack.execution
    - attack.t1059.001
logsource:
    product: windows
    category: process_creation
detection:
    selection_combined_1:
        Image|endswith:
            - '\powershell.exe'
            - '\pwsh.exe'
        CommandLine|contains:
            - ' | iex;'
            - ' | iex '
            - ' | iex}'
            - ' | IEX ;'
            - ' | IEX -Error'
            - ' | IEX (new'
            - ');IEX '
    selection_combined_2:
        CommandLine|contains:
            - '::FromBase64String'
            - '.GetString([System.Convert]::'
    selection_standalone:
        CommandLine|contains:
            - ')|iex;$'
            - ');iex($'
            - ');iex $'
            - ' | IEX | '
            - ' | iex\"'
    condition: all of selection_combined_* or selection_standalone
falsepositives:
    - Legitimate scripts that use IEX
level: high
regression_tests_path: regression_data/rules/windows/process_creation/proc_creation_win_powershell_iex_patterns/info.yml

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

4935bd48-fb4c-47f0-9802-ddcf17c4ba34

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

[[ reason ]]

What do these messages mean?

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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