Suspicious Obfuscated PowerShell Code

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

Detects suspicious UTF16 and base64 encoded and often obfuscated PowerShell code often used in command lines

title: Suspicious Obfuscated PowerShell Code
id: 8d01b53f-456f-48ee-90f6-bc28e67d4e35
status: test
description: Detects suspicious UTF16 and base64 encoded and often obfuscated PowerShell code often used in command lines
references:
    - https://app.any.run/tasks/fcadca91-3580-4ede-aff4-4d2bf809bf99/
author: Florian Roth (Nextron Systems)
date: 2022-07-11
modified: 2023-02-14
tags:
    - attack.stealth
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        CommandLine|contains:
            #  -bxor 0x
            - 'IAAtAGIAeABvAHIAIAAwAHgA'
            - 'AALQBiAHgAbwByACAAMAB4A'
            - 'gAC0AYgB4AG8AcgAgADAAeA'
            # .Invoke() |
            - 'AC4ASQBuAHYAbwBrAGUAKAApACAAfAAg'
            - 'AuAEkAbgB2AG8AawBlACgAKQAgAHwAI'
            - 'ALgBJAG4AdgBvAGsAZQAoACkAIAB8AC'
            # {1}{0}" -f
            # {0}{3}" -f
            # {2}{0}" -f
            - 'AHsAMQB9AHsAMAB9ACIAIAAtAGYAI'
            - 'B7ADEAfQB7ADAAfQAiACAALQBmAC'
            - 'AewAxAH0AewAwAH0AIgAgAC0AZgAg'
            - 'AHsAMAB9AHsAMwB9ACIAIAAtAGYAI'
            - 'B7ADAAfQB7ADMAfQAiACAALQBmAC'
            - 'AewAwAH0AewAzAH0AIgAgAC0AZgAg'
            - 'AHsAMgB9AHsAMAB9ACIAIAAtAGYAI'
            - 'B7ADIAfQB7ADAAfQAiACAALQBmAC'
            - 'AewAyAH0AewAwAH0AIgAgAC0AZgAg'
            # {1}{0}' -f
            # {0}{3}' -f
            # {2}{0}' -f
            - 'AHsAMQB9AHsAMAB9ACcAIAAtAGYAI'
            - 'B7ADEAfQB7ADAAfQAnACAALQBmAC'
            - 'AewAxAH0AewAwAH0AJwAgAC0AZgAg'
            - 'AHsAMAB9AHsAMwB9ACcAIAAtAGYAI'
            - 'B7ADAAfQB7ADMAfQAnACAALQBmAC'
            - 'AewAwAH0AewAzAH0AJwAgAC0AZgAg'
            - 'AHsAMgB9AHsAMAB9ACcAIAAtAGYAI'
            - 'B7ADIAfQB7ADAAfQAnACAALQBmAC'
            - 'AewAyAH0AewAwAH0AJwAgAC0AZgAg'
    condition: selection
falsepositives:
    - Unknown
level: high

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

f0a71ed9-0bf0-4236-b2ad-61285fe72aad

Propose edits, view related rules, and engage with the community through comments.

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

[[ reason ]]

What does this mean?

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 ]]

Community Discussion