Invoke-Obfuscation COMPRESS OBFUSCATION - PowerShell

Status: test
Severity: medium
Log source: category ps_script, product windows
Author: Timur Zinniatullin, oscd.community
Source: github.com/SigmaHQ/sigma

Detects Obfuscated Powershell via COMPRESS OBFUSCATION

MITRE ATT&CK coverage

Tactic	Techniques
Execution	`T1059.001` Command and Scripting Interpreter: PowerShell
Stealth	`T1027` Obfuscated Files or Information

Telemetry coverage

Provider	Record / event type
PowerShell	Event ID 4104: Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body

title: Invoke-Obfuscation COMPRESS OBFUSCATION - PowerShell
id: 20e5497e-331c-4cd5-8d36-935f6e2a9a07
status: test
description: Detects Obfuscated Powershell via COMPRESS OBFUSCATION
references:
    - https://github.com/SigmaHQ/sigma/issues/1009 # (Task 19)
author: Timur Zinniatullin, oscd.community
date: 2020-10-18
modified: 2022-11-29
tags:
    - attack.stealth
    - attack.t1027
    - attack.execution
    - attack.t1059.001
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection_4104:
        ScriptBlockText|contains|all:
            - 'new-object'
            - 'text.encoding]::ascii'
        ScriptBlockText|contains:
            - 'system.io.compression.deflatestream'
            - 'system.io.streamreader'
        ScriptBlockText|endswith: 'readtoend'
    condition: selection_4104
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection_4104

Stage 1: `selection_4104`

selection_4104:
    ScriptBlockText|contains|all:
        - 'new-object'
        - 'text.encoding]::ascii'
    ScriptBlockText|contains:
        - 'system.io.compression.deflatestream'
        - 'system.io.streamreader'
    ScriptBlockText|endswith: 'readtoend'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ScriptBlockText`	ends_with	`readtoend`	`field:"ScriptBlockText" kind:ends_with value:"readtoend"`
`ScriptBlockText`	match	`new-object` corpus 8 (sigma 7, splunk 1) `system.io.compression.deflatestream` `system.io.streamreader` `text.encoding]::ascii`	`field:"ScriptBlockText" kind:match`

Invoke-Obfuscation COMPRESS OBFUSCATION - PowerShell

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_4104

Indicators

Stage 0: `condition`

Stage 1: `selection_4104`