Detects dllinject module from Trickbot Trojan

Hunt Hypothesis

This hunt targets adversaries leveraging the Trickbot Trojan to establish persistence and execute malicious payloads through DLL injection within Windows processes. Proactively hunting for this behavior in Azure Sentinel is critical because early detection of these specific injection modules allows the SOC team to identify lateral movement attempts before they escalate into high-severity incidents.

YARA Rule

rule MALW_dllinject_trickbot_module : Trojan
{
meta:
author = "Marc Salinas @Bondey_m"
description = " Detects dllinject module from Trickbot Trojan"
strings:
$str_dllinj_01 = "user_pref("
$str_dllinj_02 = "<ignore_mask>"
$str_dllinj_03 = "<require_header>"
$str_dllinj_04 = "</dinj>"
condition:
all of ($str_dllinj_*)
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are specific false positive scenarios for the Trickbot DLL Injection detection rule, including suggested filters and exclusions:

• Enterprise Antivirus Real-Time Scanning

  • Scenario: Endpoint protection suites like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint frequently inject their own scanning modules (e.g., csfalcon.dll or MsMpEng.dll) into the memory space of user applications to perform real-time heuristic analysis. This behavior mimics Trickbot’s injection technique but is a standard security function.
  • Filter/Exclusion: Create an exclusion rule for processes originating from known EDR vendors (e.g., CrowdStrike Falcon Sensor, SentinelOne Agent) where the injected DLL path matches the vendor’s installation directory (e.g., C:\Program Files\CrowdStrike\ or C:\Windows\System32\Microsoft Defender Antivirus\).

• Scheduled Software Updates via SCCM/Intune

  • Scenario: During scheduled maintenance windows, Microsoft Endpoint Configuration Manager (MECM) or Microsoft Intune agents execute update tasks that inject DLLs into the ccmexec.exe process to patch applications like Adobe Reader or Java. These injections are legitimate administrative actions but trigger the detection logic due to the injection mechanism.
  • Filter/Exclusion: Exclude events where the parent process is ccmexec.exe or Microsoft.Intune.Management.Extension.exe and the target process is a known enterprise application (e.g., AcroRd32.exe, javaw.exe). Additionally, filter by time-of-day to exclude injections occurring strictly during defined maintenance windows (e.g., 01:00–04:00 local time).

• IT Support Remote Assistance Sessions

  • Scenario: When IT administrators utilize remote support