New File Association Using Exefile

Hunt Hypothesis

Detects the abuse of the exefile handler in new file association. Used for bypass of security products.

Detection Rule

Sigma (Original)

title: New File Association Using Exefile
id: 44a22d59-b175-4f13-8c16-cbaef5b581ff
status: test
description: Detects the abuse of the exefile handler in new file association. Used for bypass of security products.
references:
    - https://twitter.com/mrd0x/status/1461041276514623491
author: Andreas Hunkeler (@Karneades)
date: 2021-11-19
modified: 2023-08-17
tags:
    - attack.stealth
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|contains: 'Classes\.'
        Details: 'exefile'
    condition: selection
falsepositives:
    - Unknown
level: high

KQL (Azure Sentinel)

imRegistry
| where RegistryKey contains "Classes\\." and RegistryValueData =~ "exefile"

KQL (Microsoft 365 Defender)

DeviceRegistryEvents
| where RegistryKey contains "Classes\\." and RegistryValueData =~ "exefile"

Required Data Sources

False Positive Guidance

• Unknown

References

• https://twitter.com/mrd0x/status/1461041276514623491
• SigmaHQ Rule