Windows: Detect Microsoft Office DLL sideloading via ImageLoad of outllib.dll from nonstandard path

Alerts on outllib.dll loads from non-standard locations rather than typical Microsoft Office directories.

FreeReviewedSigma · High · v2

Product: windows
Category: image_load
Author: Nasreddine Bencherchali (Nextron Systems), Wietze Beukema (project and research) (SigmaHQ), DRL 1.1
Published: 2022-08-17
Updated: 2026-07-31

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 process DLL loads where the loaded module name ends with outllib.dll while the originating path is not one of the standard Microsoft Office installation directories. DLL sideloading can allow attackers to execute malicious code by forcing an application to load an attacker-controlled library. The detection relies on image-load telemetry that includes the loaded DLL path or filename (e.g., ImageLoaded) to distinguish nonstandard locations from expected Office directories.

Reporting behind it

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Windows: Detect Microsoft Office DLL sideloading via ImageLoad of outllib.dll from nonstandard 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-office-dll-sideloading-via-outllib-dll-image-load-outside-expected-offic-829a3bdf

title: "Windows: Detect Microsoft Office DLL sideloading via ImageLoad of outllib.dll from nonstandard path"
id: db8a6b41-6e07-4ced-ba27-5628dc8095e2
status: test
description: This rule flags process DLL loads where the loaded module name ends with outllib.dll while the originating path is not one of the standard Microsoft Office installation directories. DLL sideloading can allow attackers to execute malicious code by forcing an application to load an attacker-controlled library. The detection relies on image-load telemetry that includes the loaded DLL path or filename (e.g., ImageLoaded) to distinguish nonstandard locations from expected Office directories.
references:
  - https://hijacklibs.net/
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/image_load/image_load_side_load_office_dlls.yml
author: Nasreddine Bencherchali (Nextron Systems), Wietze Beukema (project and research), Huntrule Team
date: 2022-08-17
modified: 2023-03-15
tags:
  - attack.persistence
  - attack.privilege-escalation
  - attack.execution
  - attack.stealth
  - attack.t1574.001
logsource:
  category: image_load
  product: windows
detection:
  selection:
    ImageLoaded|endswith: \outllib.dll
  filter:
    ImageLoaded|startswith:
      - C:\Program Files\Microsoft Office\OFFICE
      - C:\Program Files (x86)\Microsoft Office\OFFICE
      - C:\Program Files\Microsoft Office\Root\OFFICE
      - C:\Program Files (x86)\Microsoft Office\Root\OFFICE
  condition: selection and not filter
falsepositives:
  - Unlikely
level: high
license: DRL-1.1
related:
  - id: 829a3bdf-34da-4051-9cf4-8ed221a8ae4f
    type: derived

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