ActiveMARKTMR5311140Trymedia

Hunt Hypothesis

This rule detects the presence of the ActiveMARKTMR5311140Trymedia YARA signature, which likely identifies a specific memory-resident component or artifact associated with a low-severity threat actor or tooling. Proactively hunting for this signature allows the SOC team to identify potential stealthy in-memory implants or early-stage footholds that may not yet trigger traditional network or endpoint alerts, thereby reducing the dwell time of low-fidelity threats within the Azure Sentinel environment.

YARA Rule

rule ActiveMARKTMR5311140Trymedia
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 79 11 7F AB 9A 4A 83 B5 C9 6B 1A 48 F9 27 B4 25 }

condition:
		$a0 at pe.entry_point
}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A developer or QA engineer is running a local test suite for a media processing library that includes a sample file named Trymedia.exe or contains the string Trymedia in its binary header for testing purposes.
  • Filter/Exclusion: Exclude processes launched from specific development directories (e.g., C:\Dev\MediaLib\tests\) or exclude processes whose parent process is a known IDE or test runner (e.g., dotnet.exe, python.exe, code.exe).
• Scenario: An IT administrator is deploying a new media management application via Group Policy or a deployment tool (like SCCM or Intune) where the installer package or temporary extraction folder contains a file matching the YARA signature due to a bundled sample or debug artifact.
  • Filter/Exclusion: Exclude processes where the parent process is a known deployment agent (e.g., CCMEXEC.EXE, IntuneManagementExtension.exe, msiexec.exe) and the image path resides in standard temporary or deployment directories (e.g., C:\Windows\Installer\, C:\ProgramData\IntuneManagementExtension\).
• Scenario: A user is running a legitimate third-party video editing or media conversion tool (e.g., Adobe Media Encoder, HandBrake, or FFmpeg-based GUIs) that loads a plugin or helper executable with a name or internal string matching the Trymedia pattern, possibly due to a shared library or a misnamed component in the vendor’s distribution.
  • Filter/Exclusion: Exclude processes where the parent process is a known media application (e.g., Adobe Media Encoder.exe, HandBrake.exe, ffmpeg.exe) and the image path is located in the vendor’s installation directory (e.g., C:\Program Files\Adobe\, C:\Program Files\HandBrake\).