HACKSTOPv110p1

Hunt Hypothesis

This hypothesis targets the presence of the HACKSTOPv110p1 YARA signature, which indicates a specific malware variant or tooling often associated with initial access or persistence mechanisms. Proactively hunting for this indicator in Azure Sentinel allows the SOC team to identify compromised endpoints or suspicious processes before the adversary can establish a foothold or escalate privileges within the environment.

YARA Rule

rule HACKSTOPv110p1
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B4 30 CD 21 86 E0 3D 00 03 73 ?? B4 2F CD 21 B4 2A CD 21 B4 2C CD 21 B0 FF B4 4C CD 21 50 B8 [2] 58 EB }

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 runs a local build script that invokes gcc or clang to compile a C/C++ project containing a main function, where the compiler driver process briefly holds a handle to the source files or intermediate object files while the linker is active.
  • Filter/Exclusion: Exclude processes where the parent process name is gcc, clang, cc1plus, or ld, and the file path matches standard build directories like /build/, /obj/, or /dist/.
• Scenario: An automated backup agent (e.g., Veeam, Commvault, or Windows Server Backup) creates a temporary shadow copy or staging file in a non-standard directory (e.g., C:\Temp\BackupStaging) that is immediately opened by the backup service for compression, causing a brief read/write lock that mimics a “hack” or injection pattern.
  • Filter/Exclusion: Exclude processes running under the service account NT AUTHORITY\SYSTEM or specific backup service accounts (e.g., VeeamBackupSvc, CommvaultBackupSvc) when the file path contains keywords like backup, staging, or shadow.
• Scenario: A corporate endpoint detection tool (e.g., CrowdStrike Falcon, Carbon Black, or Defender for Endpoint) injects a driver or DLL into a protected process to monitor its behavior, creating a temporary memory-mapped file or shared memory segment that the YARA rule interprets as a suspicious hack pattern.
  • Filter/Exclusion: Exclude processes where the parent process is a known EDR agent (e.g., FalconSensor.exe, Cb.exe, MsMpEng.exe) and the file extension is .tmp, .shm, or .mem.
• Scenario: A scheduled PowerShell job runs a custom script that uses