Indirect Inline Command Execution Via Bash.EXE

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: frack113
Source: github.com/SigmaHQ/sigma

Detects execution of Microsoft bash launcher with the "-c" flag. This can be used to potentially bypass defenses and execute Linux or Windows-based binaries directly via bash.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1202` Indirect Command Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Indirect Inline Command Execution Via Bash.EXE
id: 5edc2273-c26f-406c-83f3-f4d948e740dd
related:
    - id: 2d22a514-e024-4428-9dba-41505bd63a5b
      type: similar
status: test
description: |
    Detects execution of Microsoft bash launcher with the "-c" flag.
    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/
author: frack113
date: 2021-11-24
modified: 2023-08-15
tags:
    - attack.stealth
    - attack.t1202
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - ':\Windows\System32\bash.exe'
              - ':\Windows\SysWOW64\bash.exe'
        - OriginalFileName: 'Bash.exe'
    selection_cli:
        CommandLine|contains: ' -c '
    condition: all of selection_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith:
          - ':\Windows\System32\bash.exe'
          - ':\Windows\SysWOW64\bash.exe'
    - OriginalFileName: 'Bash.exe'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains: ' -c '

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`-c` corpus 13 (sigma 13)	`field:"CommandLine" kind:match value:" -c "`
`Image`	ends_with	`:\Windows\SysWOW64\bash.exe` corpus 2 (sigma 2) `:\Windows\System32\bash.exe` corpus 2 (sigma 2)	`field:"Image" kind:ends_with`
`OriginalFileName`	eq	`Bash.exe` corpus 4 (sigma 3, elastic 1)	`field:"OriginalFileName" kind:eq value:"Bash.exe"`