Uncommon FileSystem Load Attempt By Format.com

Hunt Hypothesis

Detects the execution of format.com with an uncommon filesystem selection that could indicate a defense evasion activity in which “format.com” is used to load malicious DLL files or other programs.

Detection Rule

Sigma (Original)

title: Uncommon FileSystem Load Attempt By Format.com
id: 9fb6b26e-7f9e-4517-a48b-8cac4a1b6c60
status: test
description: |
    Detects the execution of format.com with an uncommon filesystem selection that could indicate a defense evasion activity in which "format.com" is used to load malicious DLL files or other programs.
references:
    - https://twitter.com/0gtweet/status/1477925112561209344
    - https://twitter.com/wdormann/status/1478011052130459653?s=20
author: Florian Roth (Nextron Systems)
date: 2022-01-04
modified: 2024-05-13
tags:
    - attack.stealth
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\format.com'
        CommandLine|contains: '/fs:'
    filter_main_known_fs:
        CommandLine|contains:
            - '/fs:exFAT'
            - '/fs:FAT'
            - '/fs:NTFS'
            - '/fs:ReFS'
            - '/fs:UDF'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imProcessCreate
| where (TargetProcessName endswith "\\format.com" and TargetProcessCommandLine contains "/fs:") and (not((TargetProcessCommandLine contains "/fs:exFAT" or TargetProcessCommandLine contains "/fs:FAT" or TargetProcessCommandLine contains "/fs:NTFS" or TargetProcessCommandLine contains "/fs:ReFS" or TargetProcessCommandLine contains "/fs:UDF")))

Required Data Sources

False Positive Guidance

• Unknown

References

• https://twitter.com/0gtweet/status/1477925112561209344
• https://twitter.com/wdormann/status/1478011052130459653?s=20
• SigmaHQ Rule