Small Sieve Malware File Indicator Creation

Detects filename indicators that contain a specific typo seen used by the Small Sieve malware.

Detection logic

selection_typo_path

TargetFilename|contains|all:
  - :\Users\
  - \AppData\
TargetFilename|contains:
  - \Roaming\
  - \Local\

selection_typo_keyword

TargetFilename|contains: Microsift

selection_ioc

TargetFilename|endswith: \AppData\Local\MicrosoftWindowsOutlookDataPlus.txt

Condition

all of selection_typo_* or selection_ioc

Raw YAML

title: Small Sieve Malware File Indicator Creation
id: 39466c42-c189-476a-989f-8cdb135c163a
status: test
description: Detects filename indicators that contain a specific typo seen used by the Small Sieve malware.
references:
    - https://www.ncsc.gov.uk/static-assets/documents/malware-analysis-reports/small-sieve/NCSC-MAR-Small-Sieve.pdf
author: Nasreddine Bencherchali (Nextron Systems), X__Junior (Nextron Systems)
date: 2023-05-19
tags:
    - attack.stealth
    - attack.t1036.005
    - detection.emerging-threats
logsource:
    product: windows
    category: file_event
detection:
    selection_typo_path:
        TargetFilename|contains|all:
            - ':\Users\'
            - '\AppData\'
        TargetFilename|contains:
            - '\Roaming\'
            - '\Local\'
    selection_typo_keyword:
        TargetFilename|contains: 'Microsift'
    selection_ioc:
        TargetFilename|endswith: '\AppData\Local\MicrosoftWindowsOutlookDataPlus.txt'
    condition: all of selection_typo_* or selection_ioc
falsepositives:
    - Unlikely
level: high