Gafgyt Trojan

Hunt Hypothesis

The Gafgyt Trojan is detected through suspicious network traffic patterns indicative of command and control communication. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential botnet activity before it leads to larger-scale compromise.

YARA Rule

rule Gafgyt_Botnet_hoho : MALW
{
meta:
description = "Gafgyt Trojan"
author = "Joan Soriano / @joanbtl"
date = "2017-05-25"
version = "1.0"
MD5 = "369c7c66224b343f624803d595aa1e09"
SHA1 = "54519d2c124cb536ed0ddad5683440293d90934f"

    strings:
            $s1 = "PING"
            $s2 = "PRIVMSG"
            $s3 = "Remote IRC Bot"
            $s4 = "23.95.43.182"
    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: Legitimate scheduled job using nc (Netcat) for internal monitoring
  Filter/Exclusion: Check for nc usage in known monitoring tools like nmap or tcpdump in scheduled tasks. Exclude processes with nc that are part of internal monitoring scripts or tools.

• Scenario: System update using nc to fetch package metadata
  Filter/Exclusion: Exclude processes where nc is used by package managers like apt or yum during system updates or metadata retrieval.

• Scenario: Admin task using nc to test network connectivity
  Filter/Exclusion: Exclude nc commands used by administrators for network testing (e.g., nc -zv <host> <port>) via tools like telnet or ncat.

• Scenario: Log forwarding using nc with rsyslog or syslog-ng
  Filter/Exclusion: Exclude nc instances used by log forwarding tools like rsyslog or syslog-ng to send logs to centralized servers.

• Scenario: Internal tool using nc for inter-service communication
  Filter/Exclusion: Exclude nc usage by internal services or microservices that communicate over a private network, such as internal APIs or service meshes.