Yara rule for detection of different Spynote Variants

Hunt Hypothesis

The hypothesis is that the Yara rule detects potential Spynote malware variants based on specific signature patterns, which may indicate adversarial persistence or data exfiltration. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage espionage activities that may evade traditional detection methods.

YARA Rule

rule spynote_variants
{
    meta:
        author = "5h1vang https://analyst.koodous.com/analysts/5h1vang"
        description = "Yara rule for detection of different Spynote Variants"
        source = " http://researchcenter.paloaltonetworks.com/2016/07/unit42-spynote-android-trojan-builder-leaked/"
        rule_source = "https://analyst.koodous.com/rulesets/1710"

    strings:
        $str_1 = "SERVER_IP" nocase
        $str_2 = "SERVER_NAME" nocase
        $str_3 = "content://sms/inbox"
        $str_4 = "screamHacker" 
        $str_5 = "screamon"
    condition:
        androguard.package_name("dell.scream.application") or 
        androguard.certificate.sha1("219D542F901D8DB85C729B0F7AE32410096077CB") or
        all of ($str_*)
}

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 5 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Legitimate scheduled system maintenance task
  Description: A scheduled task using schtasks.exe or at.exe is performing routine system maintenance, which may include file operations that resemble Spynote behavior.
  Filter/Exclusion: Exclude processes initiated by schtasks.exe or at.exe with known legitimate command-line arguments or scheduled task names (e.g., WeeklyMaintenance).

• Scenario: Administrative file cleanup using PowerShell
  Description: A PowerShell script executed by an admin user is cleaning up temporary files or logs, which may include file deletions or modifications that match the Yara rule.
  Filter/Exclusion: Exclude processes with powershell.exe where the command line includes known cleanup scripts or paths to system directories (e.g., C:\Windows\Temp).

• Scenario: Software update or patch deployment
  Description: A legitimate software update or patch deployment tool (e.g., msiexec.exe, setup.exe, or patch.exe) is modifying files in a way that matches the Yara rule.
  Filter/Exclusion: Exclude processes associated with known update tools or files located in software installation directories (e.g., C:\Program Files\UpdateTool).

• Scenario: Backup or archive operations using 7-Zip or WinRAR
  Description: A backup or archive operation using tools like 7z.exe or WinRAR.exe may involve file compression or extraction that could trigger the Yara rule.
  Filter/Exclusion: Exclude processes with 7z.exe or WinRAR.exe when operating on known backup directories or temporary archive files (e.g., C:\Backup\ or C:\Temp\).

• Scenario: Log file rotation or analysis using Splunk or ELK Stack
  Description: A log rotation or