Misdat Backdoor Packed

Hunt Hypothesis

The Misdat Backdoor Packed rule detects potential adversary behavior involving the use of a packed backdoor, which may indicate the presence of a sophisticated malware payload designed to evade basic detection mechanisms. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate advanced threats that could persist undetected within the network.

YARA Rule

rule Misdat_Backdoor_Packed
{
    
    meta:
        author = "Cylance SPEAR Team"
        note = "Probably Prone to False Positive"

    strings:
        $upx = {33 2E 30 33 00 55 50 58 21}
        $send = {00 00 00 73 65 6E 64 00 00 00}
        $delphi_sec_pe = {50 45 00 00 4C 01 03 00 19 5E 42 2A}
        $shellexec = {00 00 00 53 68 65 6C 6C 45 78 65 63 75 74 65 57 00 00 00}
        
    condition:
        filesize < 100KB and $upx and $send and $delphi_sec_pe and $shellexec
}

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

• Scenario: A system administrator is using PowerShell to run a scheduled backup job that compresses files using 7-Zip.
  Filter/Exclusion: Exclude processes where the executable path contains "7-Zip" or "powershell.exe" with command-line arguments related to compression or backup tasks.

• Scenario: A DevOps engineer is deploying a Docker container using Kubernetes and the container image includes a packed binary as part of the deployment artifact.
  Filter/Exclusion: Exclude processes where the parent process is a Kubernetes scheduler or docker command, and the file path matches known container image paths.

• Scenario: A security analyst is performing a memory dump using Volatility to analyze a suspicious process, and the dump includes packed code.
  Filter/Exclusion: Exclude processes where the parent process is Volatility or ProcDump, and the file path contains "volatility" or "ProcDump.exe".

• Scenario: A system update task is using Windows Update to install a packed driver as part of a patch.
  Filter/Exclusion: Exclude processes where the parent process is wuauclt.exe (Windows Update) and the file path matches known Microsoft driver installation paths.

• Scenario: A developer is using PyInstaller to package a Python application into an executable, which results in a packed binary.
  Filter/Exclusion: Exclude processes where the executable path contains "PyInstaller" or "pyinstaller.exe", and the parent process is a Python interpreter (python.exe).