Indirect Command Execution From Script File Via Bash.EXE

SIGMA detection rule by Nasreddine Bencherchali (Nextron Systems) · NOASSERTION

Detects execution of Microsoft bash launcher without any flags to execute the content of a bash script directly. This can be used to potentially bypass defenses and execute Linux or Windows-based binaries directly via bash.

title: Indirect Command Execution From Script File Via Bash.EXE
id: 2d22a514-e024-4428-9dba-41505bd63a5b
related:
    - id: 5edc2273-c26f-406c-83f3-f4d948e740dd
      type: similar
status: test
description: |
    Detects execution of Microsoft bash launcher without any flags to execute the content of a bash script directly.
    This can be used to potentially bypass defenses and execute Linux or Windows-based binaries directly via bash.
references:
    - https://lolbas-project.github.io/lolbas/Binaries/Bash/
    - https://linux.die.net/man/1/bash
    - Internal Research
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-08-15
tags:
    - attack.stealth
    - attack.t1202
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        - Image|endswith:
              - ':\Windows\System32\bash.exe'
              - ':\Windows\SysWOW64\bash.exe'
        - OriginalFileName: 'Bash.exe'
    filter_main_cli_flag:
        CommandLine|contains:
            # Note: we're not interested in flags being passed first
            - 'bash.exe -'
            - 'bash -'
    filter_main_no_cli:
        CommandLine: null
    filter_main_empty:
        CommandLine: ''
    filter_main_no_flag:
        CommandLine:
            - 'bash.exe'
            - 'bash'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

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

8ebe7475-afa3-4de1-bdd1-d979284a706f

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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 ]]

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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 ]]

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