Windows Image Load of clfsw32.dll by svchost.exe indicating PRIVATELOG usage

Alert on svchost.exe loading clfsw32.dll, a rarely observed Windows image load pattern consistent with PRIVATELOG.

FreeReviewedSigma · High · v5

Product: windows
Category: image_load
Author: Florian Roth (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2021-09-07
Updated: 2026-07-31

ATT&CK techniques

Priv Esc → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
- T1055Process Injection
Defense Evasion
- T1055Process Injection
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags a specific Windows image load sequence where svchost.exe loads clfsw32.dll. Such module loading patterns are rarely observed under normal conditions and can indicate tool-driven stealth or misuse of legitimate components. The detection relies on image load telemetry that records the full image path for both the loading process (Image) and the loaded module (ImageLoaded).

Reporting behind it

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Windows Image Load of clfsw32.dll by svchost.exe indicating PRIVATELOG usage

Pivot detection · T1055 · 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-privatelog-image-load-svchost-exe-loading-clfsw32-dll-33a2d1dd

title: Windows Image Load of clfsw32.dll by svchost.exe indicating PRIVATELOG usage
id: 7c5ee44f-2e3a-461b-96aa-e0cbf8744a9f
status: test
description: This rule flags a specific Windows image load sequence where svchost.exe loads clfsw32.dll. Such module loading patterns are rarely observed under normal conditions and can indicate tool-driven stealth or misuse of legitimate components. The detection relies on image load telemetry that records the full image path for both the loading process (Image) and the loaded module (ImageLoaded).
references:
  - https://web.archive.org/web/20210901184449/https://www.fireeye.com/blog/threat-research/2021/09/unknown-actor-using-clfs-log-files-for-stealth.html
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/TA/PRIVATELOG/image_load_usp_svchost_clfsw32.yml
author: Florian Roth (Nextron Systems), Huntrule Team
date: 2021-09-07
modified: 2022-10-09
tags:
  - attack.privilege-escalation
  - attack.stealth
  - attack.t1055
  - detection.emerging-threats
logsource:
  category: image_load
  product: windows
detection:
  selection:
    Image|endswith: \svchost.exe
    ImageLoaded|endswith: \clfsw32.dll
  condition: selection
falsepositives:
  - Rarely observed
level: high
license: DRL-1.1
related:
  - id: 33a2d1dd-f3b0-40bd-8baf-7974468927cc
    type: derived

Convert

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