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 network compromise.

YARA Rule

rule Gafgyt_Botnet_oh : MALW
{
meta:
description = "Gafgyt Trojan"
author = "Joan Soriano / @joanbtl"
date = "2017-05-025"
version = "1.0"
MD5 = "97f5edac312de349495cb4afd119d2a5"
SHA1 = "916a51f2139f11e8be6247418dca6c41591f4557"

    strings:
            $s1 = "busyboxterrorist"
            $s2 = "BOGOMIPS"
            $s3 = "124.105.97.%d"
            $s4 = "fucknet"
    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 scheduled task running as part of system maintenance (e.g., Task Scheduler job for log rotation or disk cleanup) may trigger the Gafgyt detection due to similar process names or network behavior.
  Filter/Exclusion: Exclude processes associated with Task Scheduler or use a filter like process.name != "taskhost.exe" or process.name != "schtasks.exe".

• Scenario: Network Time Protocol (NTP) Synchronization
  Description: NTP clients (e.g., ntpd, w32time) may communicate with NTP servers using UDP port 123, which could be mistaken for Gafgyt C2 traffic.
  Filter/Exclusion: Exclude traffic on UDP port 123 using a filter like destination.port == 123 or protocol == udp and destination.port == 123.

• Scenario: Admin Tools Using Reverse DNS Lookup
  Description: Administrators may use tools like nslookup or dig to perform reverse DNS lookups, which could be flagged as suspicious network activity.
  Filter/Exclusion: Exclude processes associated with nslookup.exe or dig using a filter like process.name != "nslookup.exe" or process.name != "dig".

• Scenario: Antivirus or EDR Software Performing Network Scans
  Description: Security tools like Windows Defender or CrowdStrike Falcon may perform network scans or outbound connections to update or check for threats, which could be misclassified as Gafgyt behavior.
  Filter/Exclusion: Exclude processes from known security vendors using a filter like process.name contains "Windows Defender" or process.name contains "CrowdStrike".

• **Scenario: Legitimate IoT Device