Set Suspicious Files as System Files Using Attrib.EXE

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

Detects the usage of attrib with the "+s" option to set scripts or executables located in suspicious locations as system files to hide them from users and make them unable to be deleted with simple rights. The rule limits the search to specific extensions and directories to avoid FPs

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1564.001` Hide Artifacts: Hidden Files and Directories

Telemetry coverage

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

Rule body

title: Set Suspicious Files as System Files Using Attrib.EXE
id: efec536f-72e8-4656-8960-5e85d091345b
related:
    - id: bb19e94c-59ae-4c15-8c12-c563d23fe52b
      type: derived
status: test
description: |
    Detects the usage of attrib with the "+s" option to set scripts or executables located in suspicious locations as system files to hide them from users and make them unable to be deleted with simple rights. The rule limits the search to specific extensions and directories to avoid FPs
references:
    - https://app.any.run/tasks/c28cabc8-a19f-40f3-a78b-cae506a5c0d4
    - https://app.any.run/tasks/cfc8870b-ccd7-4210-88cf-a8087476a6d0
    - https://unit42.paloaltonetworks.com/unit42-sure-ill-take-new-combojack-malware-alters-clipboards-steal-cryptocurrency/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-06-28
modified: 2023-03-14
tags:
    - attack.stealth
    - attack.t1564.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\attrib.exe'
        - OriginalFileName: 'ATTRIB.EXE'
    selection_cli:
        CommandLine|contains: ' +s'
    selection_paths:
        CommandLine|contains:
            - ' %' # Custom Environment variable
            - '\Users\Public\'
            - '\AppData\Local\'
            - '\ProgramData\'
            - '\Downloads\'
            - '\Windows\Temp\'
    selection_ext:
        CommandLine|contains:
            - '.bat'
            - '.dll'
            - '.exe'
            - '.hta'
            - '.ps1'
            - '.vbe'
            - '.vbs'
    filter_optional_installer:
        CommandLine|contains|all:
            - '\Windows\TEMP\'
            - '.exe'
    condition: all of selection* and not 1 of filter_optional_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

all of selection* and not 1 of filter_optional_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\attrib.exe'
    - OriginalFileName: 'ATTRIB.EXE'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains: ' +s'

Stage 3: `selection_paths`

selection_paths:
    CommandLine|contains:
        - ' %'
        - '\Users\Public\'
        - '\AppData\Local\'
        - '\ProgramData\'
        - '\Downloads\'
        - '\Windows\Temp\'

Stage 4: `selection_ext`

selection_ext:
    CommandLine|contains:
        - '.bat'
        - '.dll'
        - '.exe'
        - '.hta'
        - '.ps1'
        - '.vbe'
        - '.vbs'

Stage 5: `not filter_optional_installer`

filter_optional_installer:
    CommandLine|contains|all:
        - '\Windows\TEMP\'
        - '.exe'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`CommandLine`	match	`.exe`	`excludes:CommandLine` `field:"CommandLine" value:".exe"`
`CommandLine`	match	`\Windows\TEMP\`	`excludes:CommandLine` `field:"CommandLine" value:"\Windows\TEMP\"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`%` `+s` `.bat` corpus 11 (sigma 9, elastic 1, kusto 1) `.dll` corpus 16 (sigma 16) `.exe` corpus 5 (sigma 5) `.hta` corpus 6 (sigma 6) `.ps1` corpus 4 (sigma 3, elastic 1) `.vbe` corpus 5 (sigma 5) `.vbs` corpus 7 (sigma 7) `\AppData\Local\` corpus 11 (sigma 10, elastic 1) `\Downloads\` corpus 15 (sigma 14, elastic 1) `\ProgramData\` corpus 4 (sigma 3, elastic 1) `\Users\Public\` corpus 18 (sigma 17, elastic 1) `\Windows\Temp\` corpus 13 (sigma 12, elastic 1)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\attrib.exe` corpus 5 (sigma 5)	`field:"Image" kind:ends_with value:"\attrib.exe"`
`OriginalFileName`	eq	`ATTRIB.EXE` corpus 5 (sigma 3, elastic 2)	`field:"OriginalFileName" kind:eq value:"ATTRIB.EXE"`

Set Suspicious Files as System Files Using Attrib.EXE

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli

Stage 3: selection_paths

Stage 4: selection_ext

Stage 5: not filter_optional_installer