Gafgyt Trojan

Hunt Hypothesis

The Gafgyt Trojan is detected through suspicious network traffic patterns indicative of command and control communications. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential botnet activity and reduce the risk of distributed denial-of-service attacks.

YARA Rule

rule Gafgyt_Botnet_jackmy : MALW
{
meta:
description = "Gafgyt Trojan"
author = "Joan Soriano / @joanbtl"
date = "2017-05-25"
version = "1.0"
MD5 = "419b8a10a3ac200e7e8a0c141b8abfba"
SHA1 = "5433a5768c5d22dabc4d133c8a1d192d525939d5"

    strings:
            $s1 = "PING"
            $s2 = "PONG"
            $s3 = "jackmy"         
            $s4 = "203.134.%d.%d"       
    condition:
            $s1 and $s2 and $s3 and $s4
}

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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled System Maintenance Task
  Description: A legitimate system maintenance task, such as a Windows Task Scheduler job that runs a script to update system files or clean temporary files, may trigger the Gafgyt detection due to similar network behavior.
  Filter/Exclusion: Exclude processes initiated by the Windows Task Scheduler (Task Scheduler or schtasks.exe) or use a filter on the process name or command line containing schtasks or task in the command line.

• Scenario: Network Discovery Tool Usage
  Description: Tools like nmap or arp-scan are often used for network discovery and may generate traffic patterns similar to those observed by the Gafgyt detection rule.
  Filter/Exclusion: Exclude traffic originating from known network discovery tools by checking the process name (nmap, arp-scan, etc.) or by filtering on the source IP if the tool is known to be used from a specific host.

• Scenario: Admin SSH Tunneling for Remote Access
  Description: System administrators may use SSH tunnels (e.g., ssh -L or ssh -R) to securely access internal services, which can resemble the behavior of a C2 channel used by Gafgyt.
  Filter/Exclusion: Exclude connections initiated from known admin workstations or filter based on the presence of SSH-related command-line arguments (-L, -R, etc.) in the process command line.

• Scenario: Legitimate Outbound DNS Queries
  Description: Legitimate applications or services (e.g., dnsmasq, bind, or PowerShell scripts) may perform DNS queries that could be flagged by the Gafgyt detection logic.
  Filter/Exclusion: Exclude DNS queries from known DNS servers or applications by checking the source IP, process name, or DNS query