BITS Client BitsProxy DLL Loaded By Uncommon Process

SIGMA detection rule by UnicornOfHunt · NOASSERTION

Detects an uncommon process loading the "BitsProxy.dll". This DLL is used when the BITS COM instance or API is used. This detection can be used to hunt for uncommon processes loading this DLL in your environment. Which may indicate potential suspicious activity occurring.

title: BITS Client BitsProxy DLL Loaded By Uncommon Process
id: e700ff14-1bff-4d1d-9438-738dff5f0466
status: experimental
description: |
    Detects an uncommon process loading the "BitsProxy.dll". This DLL is used when the BITS COM instance or API is used.
    This detection can be used to hunt for uncommon processes loading this DLL in your environment. Which may indicate potential suspicious activity occurring.
references:
    - https://unicornofhunt.com/2025/05/22/When-Unicorns-Go-Quiet-BITS-Jobs-and-the-Art-of-Stealthy-Transfers/
author: UnicornOfHunt
date: 2025-06-04
tags:
    - attack.persistence
    - attack.execution
    - attack.stealth
    - attack.t1197
    - detection.threat-hunting
logsource:
    category: image_load
    product: windows
detection:
    selection:
        ImageLoaded|endswith: '\BitsProxy.dll'
    filter_main_system:
        Image:
            - 'C:\Windows\System32\aitstatic.exe'
            - 'C:\Windows\System32\bitsadmin.exe'
            - 'C:\Windows\System32\desktopimgdownldr.exe'
            - 'C:\Windows\System32\DeviceEnroller.exe'
            - 'C:\Windows\System32\MDMAppInstaller.exe'
            - 'C:\Windows\System32\ofdeploy.exe'
            - 'C:\Windows\System32\RecoveryDrive.exe'
            - 'C:\Windows\System32\Speech_OneCore\common\SpeechModelDownload.exe'
            # - 'C:\Windows\System32\svchost.exe' # BITS Service - If you collect CommandLine info. Apply a filter for the specific BITS service.
            - 'C:\Windows\SysWOW64\bitsadmin.exe'
            - 'C:\Windows\SysWOW64\OneDriveSetup.exe'
            - 'C:\Windows\SysWOW64\Speech_OneCore\Common\SpeechModelDownload.exe'
    filter_optional_chrome:
        Image: 'C:\Program Files\Google\Chrome\Application\chrome.exe'
    condition: selection and not 1 of filter_main_* and not 1 of filter_optional_*
falsepositives:
    - Allowed binaries in the environment that do BITS Jobs
level: low

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

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