infostealer

Hunt Hypothesis

The infostealer detection rule identifies potential credential or data exfiltration activities by unknown malware leveraging Azure environment interactions. SOC teams should proactively hunt for this behavior to detect early-stage adversaries exploiting Azure resources for data theft.

YARA Rule

rule infostealer: amtrckr
{
	meta:
		family = "infostealer"

	condition:
		androguard.url(/koko02\.ru/)
}

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
• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate scheduled task runs a script that mimics the behavior of the infostealer YARA rule (e.g., reading files from user directories).
  Filter/Exclusion: process.name == "schtasks.exe" or file.name == "maintenance_script.ps1"

• Scenario: Admin Performing Credential Dumping for Security Audit
  Description: An admin uses tools like mimikatz or PowerView to extract credentials as part of a security audit.
  Filter/Exclusion: process.name == "mimikatz.exe" or process.name == "PowerView.ps1"

• Scenario: Legitimate Data Exfiltration via PowerShell
  Description: A script using Invoke-WebRequest or Send-MailMessage is used to transfer logs or data to a central server.
  Filter/Exclusion: process.name == "powershell.exe" and event_id == 4104 (or check for known legitimate data exfiltration patterns)

• Scenario: Software Update or Patch Deployment
  Description: A patching tool like Chocolatey or WSUS executes scripts that temporarily access sensitive directories.
  Filter/Exclusion: process.name == "choco.exe" or process.name == "wsusutil.exe"

• Scenario: User-Initiated File Transfer via Drag-and-Drop
  Description: A user manually transfers files using a tool like Robocopy or xcopy, which may trigger the rule due to file access patterns.
  Filter/Exclusion: process.name == "robocopy.exe" or process.name == "xcopy.exe"