Trivial173bySMTSMF

Hunt Hypothesis

This YARA rule identifies a specific, low-severity pattern in memory or disk artifacts, likely targeting a known benign or trivially malicious code signature. Proactively hunting for this pattern allows the SOC team to establish a baseline for common file structures and verify that these detections are not being leveraged by adversaries for stealthy persistence or initial access.

YARA Rule

rule Trivial173bySMTSMF
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB [2] 28 54 72 69 76 69 61 6C 31 37 33 20 62 79 20 53 4D 54 2F 53 4D 46 29 }

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 DevOps engineer uses Visual Studio Code or JetBrains IDEs (e.g., IntelliJ, PyCharm) to edit a large C/C++ or assembly source file. The editor’s background indexing or syntax highlighting engine may load the file into memory in a way that matches the Trivial173bySMTSMF signature, particularly if the file contains specific string constants or header structures that align with the YARA rule’s byte patterns.

  • Filter/Exclusion: Exclude processes where the parent process is code.exe, idea64.exe, or pycharm64.exe and the file extension is .c, .cpp, .h, .asm, or .rs. Alternatively, exclude if the file path resides within known development directories like C:\Users\<User>\source\ or D:\Projects\.

• Scenario: An administrator runs 7-Zip or WinRAR to extract a large archive containing embedded documentation or binary blobs (e.g., .bin, .dat, or .iso files) that were previously compressed. During the extraction process, the archive utility may hold the decompressed data in a temporary buffer or memory-mapped file that matches the YARA signature, especially if the original file contained specific magic bytes or repetitive patterns.

  • Filter/Exclusion: Exclude if the parent process is 7z.exe, 7zG.exe, WinRAR.exe, or WinRAR.exe and the file path is in a temporary directory such as C:\Users\<User>\AppData\Local\Temp\ or C:\Windows\Temp\.

• Scenario: A scheduled Windows Defender or Microsoft Security Essentials scan performs a deep inspection of a large database file (e.g., .mdb, .accdb, or .sql dump