PEBundlev244

Hunt Hypothesis

This rule detects the execution of a specific PE bundle variant, likely indicating the presence of a low-severity malware or trojan that may be used for initial access or persistence. Proactively hunting for this signature allows the SOC team to identify compromised hosts early, potentially before the bundle unpacks or establishes more complex footholds within the Azure environment.

YARA Rule

rule PEBundlev244
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 9C 60 E8 02 [3] 33 C0 8B C4 83 C0 04 93 8B E3 8B 5B FC 81 EB [2] 40 ?? 87 DD 83 BD }

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

• Legitimate Application Bundling (e.g., Electron or .NET Framework Apps)

  • Scenario: Many modern enterprise applications (such as Slack, Teams, or internal line-of-business tools) are built using frameworks like Electron or .NET, which bundle multiple DLLs, resources, and executables into a single PE file. If the YARA rule PEBundlev244 targets specific section names, import tables, or resource patterns associated with bundlers, these standard business apps will trigger the alert.
  • Filter/Exclusion: Exclude known application paths (e.g., C:\Program Files\Microsoft Teams\, C:\Users\*\AppData\Local\Slack\) or specific image hashes of trusted, signed applications. Alternatively, filter by checking if the PE file has a valid digital signature from a trusted publisher (e.g., Microsoft, Adobe, or internal CA).

• Installer Packages and Self-Extracting Archives

  • Scenario: IT departments frequently deploy software via self-extracting installers (e.g., 7-Zip SFX, NSIS, or Inno Setup). These files are PE executables that contain compressed data sections. If the rule detects specific section names (like 7zSFX or Inno Setup) or unusual section entropy, legitimate installers pushed via SCCM, PDQ Deploy, or Chocolatey will trigger the rule.
  • Filter/Exclusion: Exclude files located in common installer directories (e.g., C:\Windows\Temp\, C:\ProgramData\Chocolatey\) or filter by file extension (.exe with names containing install, setup, sfx). You can also exclude based on the presence of specific known installer signatures (e.g., NSIS or Inno Setup magic bytes) if the rule is overly broad.