Windows Rcdll.dll DLL Sideloading via Image Load Path

Flags rcdll.dll loads from unexpected locations, excluding Visual Studio and Windows Kits directories.

FreeReviewedSigma · High · v2

Product: windows
Category: image_load
Author: X__Junior (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2023-03-13
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 Windows processes that load rcdll.dll from any image path other than common Visual Studio and Windows Kits directories. Sideloading a DLL with a name like rcdll.dll can help an attacker execute unintended code while blending in with legitimate loading behavior. The detection relies on image load telemetry that records the loaded module path and matches those ending with rcdll.dll while excluding known software locations.

Reporting behind it

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Windows Rcdll.dll DLL Sideloading via Image Load 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-imageloads-rcdll-dll-from-non-vs-windows-kits-paths-6e78b74f

title: Windows Rcdll.dll DLL Sideloading via Image Load Path
id: 2b3e1dda-dce3-4b7e-9170-ae8d3d430eb1
status: test
description: This rule flags Windows processes that load rcdll.dll from any image path other than common Visual Studio and Windows Kits directories. Sideloading a DLL with a name like rcdll.dll can help an attacker execute unintended code while blending in with legitimate loading behavior. The detection relies on image load telemetry that records the loaded module path and matches those ending with rcdll.dll while excluding known software locations.
references:
  - https://www.trendmicro.com/en_us/research/23/c/iron-tiger-sysupdate-adds-linux-targeting.html
  - https://github.com/SigmaHQ/sigma/blob/master/rules/windows/image_load/image_load_side_load_rcdll.yml
author: X__Junior (Nextron Systems), Huntrule Team
date: 2023-03-13
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: \rcdll.dll
  filter:
    ImageLoaded|startswith:
      - C:\Program Files (x86)\Microsoft Visual Studio\
      - C:\Program Files (x86)\Windows Kits\
  condition: selection and not filter
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 6e78b74f-c762-4800-82ad-f66787f10c8a
    type: derived

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