Suspicious rundll32 Single-Digit DLL Execution with DllRegisterServer on Windows

Flags rundll32.exe running 1.dll with DllRegisterServer, a pattern seen in suspicious DLL execution.

FreeReviewedSigma · High · v5

Product: windows
Category: process_creation
Author: Nasreddine Bencherchali (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2023-08-31
Updated: 2026-07-31

ATT&CK techniques

Defense Evasion

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
- T1218.011Rundll32
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule identifies process creation events where rundll32.exe executes a DLL named "1.dll" and calls the export function "DllRegisterServer". Attackers may use this pattern to run malicious payloads using a legitimate Windows binary, blending execution into normal system activity. It relies on Windows process creation telemetry, matching rundll32.exe and specific command-line endings that reference the DLL and export.

Reporting behind it

Related detections9 linkedT1218.011 — drag to rearrange

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Renamed Regsvr32 or Rundll32 Loading a DLL With a Non-Standard Extension (via process_creation)

Malicious Rundll32 DllRegisterServer Execution From a User-Writable Path (via process_creation)

IMEEX Framework DLL Execution via Rundll32 Loading imaadp (via process_creation)

Suspicious Persistence via pcalua Launching rundll32 Control_RunDLL

Suspicious Rundll32 Executing DLL Start Export With Control Flags

Suspicious Rundll32 Execution of Timestamp-Named DLL

Suspicious Rundll32 Loading DLL from LocalAppData with Short Export (via process_creation)

Suspicious rundll32 Single-Digit DLL Execution with DllRegisterServer on Windows

Pivot detection · T1218.011 · 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-rundll32-executes-1-dll-dllregisterserver-via-single-digit-dll-2bd8e100

title: Suspicious rundll32 Single-Digit DLL Execution with DllRegisterServer on Windows
id: db0e9f33-7c6b-4826-8300-d286c7034d03
status: test
description: This rule identifies process creation events where rundll32.exe executes a DLL named "1.dll" and calls the export function "DllRegisterServer". Attackers may use this pattern to run malicious payloads using a legitimate Windows binary, blending execution into normal system activity. It relies on Windows process creation telemetry, matching rundll32.exe and specific command-line endings that reference the DLL and export.
references:
  - https://thedfirreport.com/2023/05/22/icedid-macro-ends-in-nokoyawa-ransomware/
  - https://thedfirreport.com/2023/08/28/html-smuggling-leads-to-domain-wide-ransomware/
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2023/Malware/IcedID/proc_creation_win_malware_icedid_rundll32_dllregisterserver.yml
author: Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2023-08-31
tags:
  - attack.stealth
  - attack.t1218.011
  - detection.emerging-threats
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    Image|endswith: \rundll32.exe
    CommandLine|endswith:
      - \1.dll, DllRegisterServer
      - " 1.dll, DllRegisterServer"
  condition: selection
falsepositives:
  - Unknown
level: high
license: DRL-1.1
related:
  - id: 2bd8e100-5b3b-4b6a-bbb5-b129d3ddddc5
    type: derived

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