AWL Bypass with Winrm.vbs and Malicious WsmPty.xsl/WsmTxt.xsl

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: Julia Fomina, oscd.community
Source: github.com/SigmaHQ/sigma

Detects execution of attacker-controlled WsmPty.xsl or WsmTxt.xsl via winrm.vbs and copied cscript.exe (can be renamed)

Known false positives

Unlikely

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1216` System Script Proxy Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: AWL Bypass with Winrm.vbs and Malicious WsmPty.xsl/WsmTxt.xsl
id: 074e0ded-6ced-4ebd-8b4d-53f55908119d
status: test
description: Detects execution of attacker-controlled WsmPty.xsl or WsmTxt.xsl via winrm.vbs and copied cscript.exe (can be renamed)
references:
    - https://posts.specterops.io/application-whitelisting-bypass-and-arbitrary-unsigned-code-execution-technique-in-winrm-vbs-c8c24fb40404
author: Julia Fomina, oscd.community
date: 2020-10-06
modified: 2022-10-09
tags:
    - attack.stealth
    - attack.t1216
logsource:
    category: process_creation
    product: windows
detection:
    contains_format_pretty_arg:
        CommandLine|contains:
            - 'format:pretty'
            - 'format:"pretty"'
            - 'format:"text"'
            - 'format:text'
    image_from_system_folder:
        Image|startswith:
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
    contains_winrm:
        CommandLine|contains: 'winrm'
    condition: contains_winrm and (contains_format_pretty_arg and not image_from_system_folder)
falsepositives:
    - Unlikely
level: medium

Stages and Predicates

Stage 0: `condition`

contains_winrm and (contains_format_pretty_arg and not image_from_system_folder)

Stage 1: `contains_winrm`

contains_winrm:
    CommandLine|contains: 'winrm'

Stage 2: `contains_format_pretty_arg`

contains_format_pretty_arg:
    CommandLine|contains:
        - 'format:pretty'
        - 'format:"pretty"'
        - 'format:"text"'
        - 'format:text'

Stage 3: `not image_from_system_folder`

image_from_system_folder:
    Image|startswith:
        - 'C:\Windows\System32\'
        - 'C:\Windows\SysWOW64\'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	starts_with	`C:\Windows\SysWOW64\`	`excludes:Image` `field:"Image" value:"C:\Windows\SysWOW64\"`
`Image`	starts_with	`C:\Windows\System32\`	`excludes:Image` `field:"Image" value:"C:\Windows\System32\"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`format:"pretty"` `format:"text"` `format:pretty` `format:text` `winrm` corpus 2 (sigma 2)	`field:"CommandLine" kind:match`