Fuery
Table of Contents
Overview
Fuery (cataloged across endpoint security telemetry under signatures including Trojan:Win32/Fuery, Trojan:Win32/Fuery.A!cl, and Trojan.Fuery) is a prominent cloud-based heuristic detection by Microsoft Defender identifying stealthy polymorphic trojans, droppers, and backdoors active since 2017. Binaries flagged under the Fuery signature employ advanced evasive techniques such as process hollowing into svchost.exe, dynamic API resolution via PEB hashing, and anti-debugging checks to bypass static file scanners and automated sandbox analysis. Fuery droppers are frequently deployed in cybercrime campaigns to establish initial endpoint access, download secondary payloads (including information stealers and ransomware), and disable local security tools.
Known aliases
Threat reports may refer to this family under multiple names:
Family Pedigree & Lineage
Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:
Known Derivatives & Downstream Variants: Trojan:Win32/Fuery.A!Cl · Trojan:Win32/Fuery.B!Cl
MITRE ATT&CK Techniques
This family has been observed using the following ATT&CK techniques: T1059.003 · T1055.012 · T1562.001 · T1105 · T1547.001
Tactical Mitigations
Based on the techniques used by this family, consider the following defensive strategies:
- T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
- T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.
MITRE D3FEND™ Defensive Countermeasures
Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-PHA | Process Hollowing Analysis | Detect | T1055.012 | Inspect unbacked executable memory regions (PAGE_EXECUTE_READWRITE) for replaced PE image headers inside legitimate host processes. |
D3-PBA | Process Spawn Analysis | Detect | T1059.003 | Inspect command-line arguments and anomalous parent-child relationships spawning from cmd.exe. |
D3-NTI | Network Traffic Inspection | Detect | T1105 | Inspect deep packet payloads for anomalous staging binaries and unauthorized egress protocols. |
D3-RPM | Registry Persistence Monitoring | Detect | T1547.001 | Audit and restrict write privileges to user and machine-level Registry Run/RunOnce keys using Endpoint Privilege Management. |
D3-STA | Security Tool Anti-Tamper Enforcement | Harden | T1562.001 | Block unauthorized modification of antivirus registry flags and prevent stopping security agent services. |
Tiered Detection Rules (Cisco CAIRN Model)
Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:
Tier 1 Primitive Artifact Rule (Fast Triage)
Matches raw strings and file markers. Vulnerable to binary repacking and simple obfuscation.
rule MALWARE_WIN_FUERY_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Fuery"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "fuery" ascii wide nocase
$s2 = "trojan:win32/fuery" ascii wide nocase
$s3 = "trojan:win32/fuery.a!cl" ascii wide nocase
$s4 = "trojan:win32/fuery.b!cl" ascii wide nocase
$s5 = "win32/fuery" ascii wide nocase
$s6 = "trojan.fuery" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Tier 2 Behavioral Context Rule (Process Chains & Sigma)
Tracks parent-child process anomalies and suspicious scripting telemetry. Resilient against file renames.
title: SystemHelpDesk Detection - Fuery (Trojan) Execution & Triage
id: a7987f44-555d-5351-be73-0ccf80885bab
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Fuery malware family. Detects suspicious execution from temporary user
directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/fuery
- https://malware-families-catalog.systemhelpdesk.com/defensive/downloader-dropper-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.trojan
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1059_003
- attack.t1055_012
- attack.t1562_001
- attack.t1105
- attack.t1547_001
logsource:
category: process_creation
product: windows
detection:
selection_process:
Image|endswith:
- \cmd.exe
- \powershell.exe
- \cscript.exe
- \wscript.exe
CommandLine|contains:
- AppData\Local\Temp
- -WindowStyle Hidden
- /e:jscript
- bitsadmin /transfer
condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: mediumTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_FUERY_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Fuery tradecraft"
tier = "T3 - Attribution Fingerprint"
confidence = "High (Confirmed Family Signature)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
// Core family identifier & heuristic payload signatures
$attrib_str = "fuery" ascii wide nocase
$pe_magic = "MZ" ascii
$net_marker = "http" ascii nocase
condition:
uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}References & External Analysis
- Microsoft Defender Threat Encyclopedia - Trojan:Win32/Fuery
- Trend Micro Threat Encyclopedia - Trojan.Win32.Fuery
- Search "fuery" on VirusTotal (External Analysis)
- Search "fuery" on Any.Run (Sandbox Sandbox)
- Search "fuery" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Trojan:Win32/Fuery?
Fuery is a Microsoft Defender cloud heuristic detection identifying evasive, polymorphic Windows trojans and initial access loaders.
What does the '!cl' suffix in Fuery.A!cl mean?
The '!cl' suffix denotes Cloud-based heuristic classification, where cloud telemetry identified malicious behavioral patterns in an unknown binary.
What malicious actions are performed by Fuery binaries?
Fuery binaries hollow code into svchost.exe, disable Windows Defender services, establish persistence, and download secondary payloads.
How is Fuery distributed to victim machines?
It is delivered through malicious spam attachments, cracked software keygens, and exploit kit drive-by downloads.
How should an enterprise respond to a Fuery detection?
Isolate the endpoint, check EDR logs for spawned child processes and hollowed svchost.exe instances, and conduct full remediation.
How do I remove Fuery from Windows?
Manual removal of Fuery is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.
What are the main symptoms of a Fuery infection?
Symptoms of Fuery can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.
Protect Your Network Against Trojans
Want to prevent Fuery and similar threats from compromising your organization? Read our comprehensive defensive guide: Banking Trojan Protection for Businesses.
📣 Threat Intel Correction or Update?
Notice an outdated IOC, unlisted alias, or disputed attribution? Threat researchers are invited to propose an update on GitHub or contact the SystemHelpDesk research desk. All community revisions are credited in our public CHANGELOG.
Machine-readable
Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/fuery.json
Ecosystem & Interactive Environments
This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.