Windows Process Loaded BitsProxy.dll via Uncommon Image

Alert on image loads of BitsProxy.dll by processes outside an allowlist of common Windows BITS-related executables.

FreeReviewedSigma · Low · v5

Product: windows
Category: image_load
Author: UnicornOfHunt (SigmaHQ), DRL 1.1
Published: 2025-06-04
Updated: 2026-07-31

ATT&CK techniques

Execution → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
- T1197BITS Jobs
Persistence
- T1197BITS Jobs
Priv Esc
Defense Evasion
- T1197BITS Jobs
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags events where an uncommon Windows process loads BitsProxy.dll, a DLL associated with BITS COM instance/API usage. Attackers may use BITS-related components to blend activity with legitimate system behavior, so unexpected process participation is a useful hunting signal. The detection relies on image load telemetry that records the loaded module path ending in \BitsProxy.dll, and it filters out several known legitimate loader binaries and Chrome.

Reporting behind it

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Suspicious PowerShell BITS Transfer of DLL Payload via process_creation

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Suspicious Remote Script Transfer via Bitsadmin (via process_creation)

Windows Process Loaded BitsProxy.dll via Uncommon Image

Pivot detection · T1197 · 9 related

Changelog

v5
Candidate ingested via manual entry.2026-07-31
v4
Candidate ingested via manual entry.2026-07-31
v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

windows-uncommon-process-loads-bitsproxy-dll-via-image-load-e700ff14

title: Windows Process Loaded BitsProxy.dll via Uncommon Image
id: 968afe67-4420-4aad-974d-1fa47090ceda
status: experimental
description: This rule flags events where an uncommon Windows process loads BitsProxy.dll, a DLL associated with BITS COM instance/API usage. Attackers may use BITS-related components to blend activity with legitimate system behavior, so unexpected process participation is a useful hunting signal. The detection relies on image load telemetry that records the loaded module path ending in \BitsProxy.dll, and it filters out several known legitimate loader binaries and Chrome.
references:
  - https://unicornofhunt.com/2025/05/22/When-Unicorns-Go-Quiet-BITS-Jobs-and-the-Art-of-Stealthy-Transfers/
  - https://github.com/SigmaHQ/sigma/blob/master/rules-threat-hunting/windows/image_load/image_load_dll_bitsproxy_load_by_uncommon_process.yml
author: UnicornOfHunt, Huntrule Team
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\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
license: DRL-1.1
related:
  - id: e700ff14-1bff-4d1d-9438-738dff5f0466
    type: derived

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