Gafgyt Trojan

Hunt Hypothesis

The Gafgyt Trojan is detected through suspicious network traffic patterns indicative of command and control communication, which may suggest the presence of a botnet. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate potential large-scale distributed attacks before they cause significant damage.

YARA Rule

rule Gafgyt_Botnet_bash : MALW
{
meta:
description = "Gafgyt Trojan"
author = "Joan Soriano / @joanbtl"
date = "2017-05-25"
version = "1.0"
MD5 = "c8d58acfe524a09d4df7ffbe4a43c429"
SHA1 = "b41fefa8470f3b3657594af18d2ea4f6ac4d567f"

    strings:
            $s1 = "PONG!"
            $s2 = "GETLOCALIP"
            $s3 = "HTTPFLOOD"
            $s4 = "LUCKYLILDUDE"
    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 running a known Gafgyt variant for testing purposes
  Filter/Exclusion: process.name != "gafgyt-test-tool" or process.parent.name == "task scheduler"

• Scenario: System update or patching tool that includes a Gafgyt binary as part of a multi-component update package
  Filter/Exclusion: process.name != "update_manager.exe" or process.parent.name == "windows update"

• Scenario: Admin using a network scanning tool that includes Gafgyt for penetration testing
  Filter/Exclusion: process.name != "nmap.exe" or process.parent.name == "penetration_testing_tool"

• Scenario: False positive from a third-party security tool that bundles Gafgyt as part of its own payload
  Filter/Exclusion: process.name != "third_party_antivirus.exe" or process.parent.name == "security_tool"

• Scenario: Legitimate system process that shares the same hash as a known Gafgyt variant due to signature overlap
  Filter/Exclusion: file.hash != "known_gafgyt_hash" or file.type == "system_binary"