Atbroker Registry Change

Hunt Hypothesis

Detects creation/modification of Assistive Technology applications and persistence with usage of ‘at’

Detection Rule

Sigma (Original)

title: Atbroker Registry Change
id: 9577edbb-851f-4243-8c91-1d5b50c1a39b
status: test
description: Detects creation/modification of Assistive Technology applications and persistence with usage of 'at'
references:
    - http://www.hexacorn.com/blog/2016/07/22/beyond-good-ol-run-key-part-42/
    - https://lolbas-project.github.io/lolbas/Binaries/Atbroker/
author: Mateusz Wydra, oscd.community
date: 2020-10-13
modified: 2023-01-19
tags:
    - attack.privilege-escalation
    - attack.stealth
    - attack.t1218
    - attack.persistence
    - attack.t1547
logsource:
    category: registry_event
    product: windows
detection:
    selection:
        TargetObject|contains:
            - 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs'
            - 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration'
    filter_atbroker:
        Image: 'C:\Windows\system32\atbroker.exe'
        TargetObject|contains: '\Microsoft\Windows NT\CurrentVersion\Accessibility\Configuration'
        Details: '(Empty)'
    filter_uninstallers:
        Image|startswith: 'C:\Windows\Installer\MSI'
        TargetObject|contains: 'Software\Microsoft\Windows NT\CurrentVersion\Accessibility\ATs'
    condition: selection and not 1 of filter_*
falsepositives:
    - Creation of non-default, legitimate at usage
level: medium

KQL (Azure Sentinel)

imRegistry
| where (RegistryKey contains "Software\\Microsoft\\Windows NT\\CurrentVersion\\Accessibility\\ATs" or RegistryKey contains "Software\\Microsoft\\Windows NT\\CurrentVersion\\Accessibility\\Configuration") and (not(((ActingProcessName =~ "C:\\Windows\\system32\\atbroker.exe" and RegistryKey contains "\\Microsoft\\Windows NT\\CurrentVersion\\Accessibility\\Configuration" and RegistryValueData =~ "(Empty)") or (ActingProcessName startswith "C:\\Windows\\Installer\\MSI" and RegistryKey contains "Software\\Microsoft\\Windows NT\\CurrentVersion\\Accessibility\\ATs"))))

Required Data Sources

False Positive Guidance

• Creation of non-default, legitimate at usage

MITRE ATT&CK Context

• Tactic: Privilege Escalation
• Tactic: Persistence
• Technique: T1218 — T1218
• Technique: T1547 — T1547

References

• http://www.hexacorn.com/blog/2016/07/22/beyond-good-ol-run-key-part-42/
• https://lolbas-project.github.io/lolbas/Binaries/Atbroker/
• SigmaHQ Rule