Windows DLL Sideloading Indicator: JsSchHlp Loads JSESPR.dll from Untrusted Path

Alerts on unexpected loads of \JSESPR.dll, indicating possible DLL sideloading outside the Justsystem JsSchHlp directory.

FreeReviewedSigma · Medium · v2

Product: windows
Category: image_load
Author: frack113 (SigmaHQ), DRL 1.1
Published: 2022-12-14
Updated: 2026-07-31

Analysis Detection

ATT&CK techniques

Execution → Defense Evasion

Recon
Resource Dev
Initial Access
Execution
- T1574.001DLL
Persistence
- T1574.001DLL
Priv Esc
- T1574.001DLL
Defense Evasion
- T1574.001DLL
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags cases where a process loads the DLL named JSESPR.dll, but the DLL load path is not the expected JsSchHlp directory under Program Files\Common Files\Justsystem. Attackers may use DLL sideloading to execute malicious code under the guise of a legitimate application component. The detection relies on Windows image load telemetry that provides the loaded DLL filename and full load path.

Reporting behind it

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Windows DLL Sideloading Indicator: JsSchHlp Loads JSESPR.dll from Untrusted Path

Pivot detection · T1574.001 · 9 related

Changelog

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-dll-sideloading-suspicion-via-image-load-of-jsschhlp-dll-68654bf0

title: "Windows DLL Sideloading Indicator: JsSchHlp Loads JSESPR.dll from Untrusted Path"
id: 34d7869c-9343-48d0-8ebb-c7eb248db864
status: test
description: This rule flags cases where a process loads the DLL named JSESPR.dll, but the DLL load path is not the expected JsSchHlp directory under Program Files\Common Files\Justsystem. Attackers may use DLL sideloading to execute malicious code under the guise of a legitimate application component. The detection relies on Windows image load telemetry that provides the loaded DLL filename and full load path.
references:
  - https://www.welivesecurity.com/2022/12/14/unmasking-mirrorface-operation-liberalface-targeting-japanese-political-entities/
  - http://www.windowexe.com/bbs/board.php?q=jsschhlp-exe-c-program-files-common-files-justsystem-jsschhlp-jsschhlp
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/image_load/image_load_side_load_jsschhlp.yml
author: frack113, Huntrule Team
date: 2022-12-14
tags:
  - attack.persistence
  - attack.privilege-escalation
  - attack.execution
  - attack.stealth
  - attack.t1574.001
logsource:
  category: image_load
  product: windows
detection:
  selection:
    ImageLoaded|endswith: \JSESPR.dll
  filter:
    ImageLoaded|startswith: C:\Program Files\Common Files\Justsystem\JsSchHlp\
  condition: selection and not filter
falsepositives:
  - Unknown
level: medium
license: DRL-1.1
related:
  - id: 68654bf0-4412-43d5-bfe8-5eaa393cd939
    type: derived

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