aPack 082 d EXE

Hunt Hypothesis

This rule detects the presence of the aPack 082 executable, a component of the aPack malware family often used for initial access or payload delivery. Proactively hunting for this artifact in Azure Sentinel allows the SOC to identify compromised endpoints or staging areas before the malware can establish persistence or execute further malicious actions.

YARA Rule

rule aPack_082_d_EXE: PEiD
{
    strings:
        $a = { 8C CB BA 00 00 03 DA 8D 87 00 00 FC 33 F6 33 FF 48 4B 8E C0 8E DB B9 08 00 F3 A5 4A 75 EE 8E C3 8E D8 33 FF BE 2F 00 05 00 00 0E 50 6A 00 CB }
    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

• Legitimate Software Installer or Updater: Many commercial applications (e.g., Adobe Creative Cloud, Microsoft Office, or Java) use custom installers or updaters that may pack their executable files to reduce size or protect intellectual property. These often reside in C:\Program Files\ or C:\ProgramData\ and are executed by standard user or admin accounts.

  • Filter/Exclusion: Exclude files located in standard installation directories (C:\Program Files\, C:\Program Files (x86)\, C:\ProgramData\) where the parent process is a known installer service (e.g., msiexec.exe, setup.exe, or vendor-specific installers like AdobeUpdateService.exe).

• Antivirus or Security Tool Self-Update: Security products like CrowdStrike Falcon, Carbon Black, or SentinelOne often run background update agents or engine refresh tasks that may use packed executables to ensure integrity and prevent tampering. These processes typically run under a dedicated service account (e.g., FalconService, CarbonBlackService) and reside in vendor-specific directories.

  • Filter/Exclusion: Exclude processes where the executable path contains vendor-specific strings (e.g., \CrowdStrike\, \CarbonBlack\, \SentinelOne\) and the process name matches known update or service binaries (e.g., FalconUpdateService.exe, cbengine.exe).

• Scheduled Maintenance or Backup Jobs: Enterprise backup solutions (e.g., Veeam, Commvault, or Acronis) or database maintenance scripts (e.g., SQL Server Agent jobs) may invoke packed helper executables or temporary agents to perform disk operations, compression, or encryption tasks. These are often triggered by Task Scheduler and run under a service account.

  • Filter/Exclusion: Exclude executions where the parent process is Task Scheduler (`