Use NTFS Short Name in Command Line

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: frack113, Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detect use of the Windows 8.3 short name. Which could be used as a method to avoid command-line detection

Known false positives

Applications could use this notation occasionally which might generate some false positives. In that case Investigate the parent and child process.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1564.004` Hide Artifacts: NTFS File Attributes

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: Use NTFS Short Name in Command Line
id: dd6b39d9-d9be-4a3b-8fe0-fe3c6a5c1795
related:
    - id: 3ef5605c-9eb9-47b0-9a71-b727e6aa5c3b
      type: similar
status: test
description: Detect use of the Windows 8.3 short name. Which could be used as a method to avoid command-line detection
references:
    - https://www.acunetix.com/blog/articles/windows-short-8-3-filenames-web-security-problem/
    - https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/cc959352(v=technet.10)
    - https://twitter.com/jonasLyk/status/1555914501802921984
author: frack113, Nasreddine Bencherchali (Nextron Systems)
date: 2022-08-05
modified: 2022-09-21
tags:
    - attack.stealth
    - attack.t1564.004
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        CommandLine|contains:
            - '~1.exe'
            - '~1.bat'
            - '~1.msi'
            - '~1.vbe'
            - '~1.vbs'
            - '~1.dll'
            - '~1.ps1'
            - '~1.js'
            - '~1.hta'
            - '~2.exe'
            - '~2.bat'
            - '~2.msi'
            - '~2.vbe'
            - '~2.vbs'
            - '~2.dll'
            - '~2.ps1'
            - '~2.js'
            - '~2.hta'
    filter:
        - ParentImage|endswith:
              - '\WebEx\WebexHost.exe'
              - '\thor\thor64.exe'
        - CommandLine|contains: 'C:\xampp\vcredist\VCREDI~1.EXE'
    condition: selection and not filter
falsepositives:
    - Applications could use this notation occasionally which might generate some false positives. In that case Investigate the parent and child process.
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    CommandLine|contains:
        - '~1.exe'
        - '~1.bat'
        - '~1.msi'
        - '~1.vbe'
        - '~1.vbs'
        - '~1.dll'
        - '~1.ps1'
        - '~1.js'
        - '~1.hta'
        - '~2.exe'
        - '~2.bat'
        - '~2.msi'
        - '~2.vbe'
        - '~2.vbs'
        - '~2.dll'
        - '~2.ps1'
        - '~2.js'
        - '~2.hta'

Stage 2: `not filter`

filter:
    - ParentImage|endswith:
          - '\WebEx\WebexHost.exe'
          - '\thor\thor64.exe'
    - CommandLine|contains: 'C:\xampp\vcredist\VCREDI~1.EXE'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`CommandLine`	match	`C:\xampp\vcredist\VCREDI~1.EXE`	`excludes:CommandLine` `field:"CommandLine" value:"C:\xampp\vcredist\VCREDI~1.EXE"`
`ParentImage`	ends_with	`\WebEx\WebexHost.exe`	`excludes:ParentImage` `field:"ParentImage" value:"\WebEx\WebexHost.exe"`
`ParentImage`	ends_with	`\thor\thor64.exe`	`excludes:ParentImage` `field:"ParentImage" value:"\thor\thor64.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`~1.bat` `~1.dll` `~1.exe` `~1.hta` `~1.js` `~1.msi` `~1.ps1` `~1.vbe` `~1.vbs` `~2.bat` `~2.dll` `~2.exe` `~2.hta` `~2.js` `~2.msi` `~2.ps1` `~2.vbe` `~2.vbs`	`field:"CommandLine" kind:match`