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

Status: test
Severity: medium
Log source: category file_event, 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 11: FileCreate

Rule body

title: AWL Bypass with Winrm.vbs and Malicious WsmPty.xsl/WsmTxt.xsl - File
id: d353dac0-1b41-46c2-820c-d7d2561fc6ed
related:
    - id: 074e0ded-6ced-4ebd-8b4d-53f55908119d
      type: derived
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: 2022-11-28
tags:
    - attack.stealth
    - attack.t1216
logsource:
    product: windows
    category: file_event
detection:
    system_files:
        TargetFilename|endswith:
            - 'WsmPty.xsl'
            - 'WsmTxt.xsl'
    in_system_folder:
        TargetFilename|startswith:
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
    condition: system_files and not in_system_folder
falsepositives:
    - Unlikely
level: medium

Stages and Predicates

Stage 0: `condition`

system_files and not in_system_folder

Stage 1: `system_files`

system_files:
    TargetFilename|endswith:
        - 'WsmPty.xsl'
        - 'WsmTxt.xsl'

Stage 2: `not in_system_folder`

in_system_folder:
    TargetFilename|startswith:
        - 'C:\Windows\System32\'
        - 'C:\Windows\SysWOW64\'

Exclusions

The rule actively suppresses these predicates.

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

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`TargetFilename`	ends_with	`WsmPty.xsl` `WsmTxt.xsl`	`field:"TargetFilename" kind:ends_with`