Trivial173 by SMTSMF additional

Hunt Hypothesis

This hypothesis targets the execution of specific malicious or suspicious code patterns identified by the YARA signature “Trivial173_by_SMTSMF_additional,” which often indicates the presence of known malware families or exploit kits within host processes. Proactively hunting for these signatures in Azure Sentinel allows the SOC to identify low-severity but potentially persistent threats that may evade standard behavioral detections, ensuring early containment of targeted intrusions.

YARA Rule

rule Trivial173_by_SMTSMF_additional: PEiD
{
    strings:
        $a = { EB ?? ?? 28 54 72 69 76 69 61 6C 31 37 33 20 62 79 20 53 4D 54 2F 53 4D 46 29 }
    condition:
        $a 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 DevOps engineer uses 7-Zip (7z.exe) or WinRAR (WinRAR.exe) to compress large log files or backup archives on a file server or build agent. The YARA rule likely flags the specific byte patterns of compressed data or the executable itself if it scans memory or disk.
  • Filter/Exclusion: Exclude processes where the parent process is 7z.exe, WinRAR.exe, or tar.exe (on Linux/WSL), or exclude file paths ending in .zip, .7z, or .rar if the rule inspects file headers.
• Scenario: An IT administrator runs Sysinternals tools like Process Monitor (procmon.exe) or Process Explorer (procexp.exe) to troubleshoot application performance issues. These tools often hook into system calls or inspect memory, which can trigger generic YARA signatures that look for unusual API usage or memory structures.
  • Filter/Exclusion: Exclude processes named procmon.exe, procexp.exe, or poolmon.exe from the Sysinternals suite, and restrict the detection to non-administrative user accounts or specific non-IT departments.
• Scenario: A scheduled PowerShell job or a CI/CD pipeline agent (e.g., Jenkins, Azure DevOps) executes a script that downloads and executes a temporary installer or updates a dependency library (e.g., npm install, pip install, or dotnet restore). The YARA rule may flag the transient executable or the specific memory layout of the package manager during execution.
  • Filter/Exclusion: Exclude processes running from standard CI/CD agent directories (e.g., C:\Program Files\Jenkins\, C:\agent\) or exclude parent processes like node.exe, python.exe, or pwsh.exe