TangoAlfa

Hunt Hypothesis

This detection identifies potential adversary activity characterized by specific file patterns defined by the TangoAlfa YARA signature, which may indicate early-stage reconnaissance or benign tooling often missed by high-severity alerts. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to validate these low-fidelity signals against baseline operations, ensuring that subtle indicators of compromise are not overlooked before they escalate into significant incidents.

YARA Rule

rule TangoAlfa
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - trig@novetta.com"

	strings:
		// $firewall is a shared code string
		$firewall = "%sd.e%sc n%ssh%srewa%s ad%s po%sop%sing T%s %d \"%s\""
		
		$testStatus1 = "*****[Start Test -> %s:%d]" wide
		$testStatus2 = "*****[Relay Connect " wide
		$testStatus3 = "*****[Listen Port %d] - " wide
		$testStatus4 = "*****[Error Socket]" wide
		$testStatus5 = "*****[End Test]" wide

	condition:
		2 of them
}

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 6 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the TangoAlfa detection rule in an enterprise environment, including suggested filters or exclusions:

• Antivirus Definition Updates via WSUS/SCCM

  • Scenario: The Windows Update Agent (wuauclt.exe) or SCCM Client (ccmexec.exe) downloads and executes a new definition package. This process often involves unpacking compressed archives containing numerous executable scripts, which the YARA rule may flag as suspicious behavior due to high entropy or specific string patterns resembling known malware families.
  • Filter/Exclusion: Create an exclusion for the parent processes wuauclt.exe, ccmexec.exe, and MsMpEng.exe (Windows Defender) when they are spawning child processes in the %ProgramData%\Microsoft\Windows Defender\Updates or %Temp% directories.

• Scheduled PowerShell Compliance Audits

  • Scenario: A nightly scheduled task named “SecurityComplianceCheck” runs a complex PowerShell script (powershell.exe) that dynamically loads modules and generates JSON reports. The rule might trigger on the script’s self-modifying behavior or the creation of temporary .ps1 files in C:\Scripts\Audit, mistaking the legitimate code injection for a living-off-the-land attack.
  • Filter/Exclusion: Exclude events where the command line contains specific known script paths (e.g., *SecurityComplianceCheck.ps1) and the user context is a dedicated service account such as svc-audit-runner or DOMAIN\AuditService.

• Enterprise Software Deployment via Ansible/Terraform

  • Scenario: During a patch Tuesday deployment, an automation controller (e.g., ansible-playbook.exe running on a jump host) pushes configuration updates to endpoints. This involves the temporary creation and execution of binary artifacts in `C:\