grelos v

Hunt Hypothesis

The rule detects potential adversarial activity involving the use of a custom YARA signature associated with the grelos_v threat, which may indicate the presence of unknown malicious artifacts. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage threats that may evade traditional detection methods.

YARA Rule

rule grelos_v {
    strings: $ = "var grelos_v"
    condition: any 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
• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate system maintenance task, such as a Windows Task Scheduler job, is running and matches the YARA rule due to similar string patterns.
  Filter/Exclusion: Check for ProcessName containing schtasks.exe or TaskScheduler in the process tree.

• Scenario: Antivirus or Endpoint Protection Scan
  Description: A security tool like Microsoft Defender, Kaspersky, or Bitdefender is performing a full system scan, and its internal components match the YARA rule.
  Filter/Exclusion: Filter by ProcessName containing MsMpEng.exe, KavStub.exe, or bdagent.exe.

• Scenario: Log Management Tool Processing
  Description: A log management tool like Splunk, ELK Stack, or Graylog is processing logs and generates output that matches the rule.
  Filter/Exclusion: Check for ProcessName containing splunkd.exe, logstash, or graylog2-server.

• Scenario: Database Backup Job
  Description: A database backup job using MySQL, PostgreSQL, or SQL Server is running and generates output that triggers the rule.
  Filter/Exclusion: Filter by ProcessName containing mysqldump, pg_dump, or sqlbackup.exe.

• Scenario: Network Monitoring Tool Traffic
  Description: A network monitoring tool like Wireshark, tcpdump, or PRTG is capturing and analyzing network traffic, which may contain patterns matching the rule.
  Filter/Exclusion: Check for ProcessName containing wireshark.exe, tcpdump, or prtg.exe.