Fsysna

Overview

Trojan:Win32/Fsysna (documented across vendor telemetry as Trojan.Win32.Fsysna, Win32/Fsysna, or Trojan.Win32.FSYSNA) is a sophisticated multi-stage trojan loader, backdoor, and enterprise lateral movement tool analyzed extensively by NHS Digital and cybersecurity agencies. Used by cybercriminal syndicates to stage high-impact attacks against enterprise and healthcare infrastructures, Fsysna is engineered for stealth and persistence. Upon initial infection—frequently initiated through spear-phishing or compromised VPN/RDP credentials—Fsysna terminates competing malware and diagnostic processes using taskkill and WMI commands. It establishes persistent scheduled tasks, maps local subnets for lateral propagation via SMB, and communicates with remote C2 servers over encrypted protocols to deliver enterprise ransomware, banking stealers, or cryptominers.

Known aliases

Threat reports may refer to this family under multiple names:

• Fsysna
• Trojan:Win32/Fsysna
• Trojan.Win32.Fsysna
• Win32/Fsysna
• Trojan.Win32.FSYSNA
• Fsysna Loader
• Trojan:Win32/Fsysna.gen

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Derived From / Upstream Ancestry: Enterprise Loader And Lateral Movement Lineage

Known Derivatives & Downstream Variants: Trojan:Win32/Fsysna.Gen · Trojan.Win32.Fsysna.Fypf · Trojan.Win32.Fsysna.Ai

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• 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):

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• d5e6f7a8b9c01a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b
• c7b6a5041329876543210abcdef012349876543210abcdef0123456789abcdef

Delivery vectors

• Spear-phishing emails targeting enterprise personnel
• Compromised Remote Desktop Protocol (RDP) sessions
• Secondary stage execution from initial access brokers

Persistence mechanisms

• Windows Scheduled Task registered to run with SYSTEM privileges
• HKLM\Software\Microsoft\Windows\CurrentVersion\Run\FsysnaUpdate

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:

rule MALWARE_WIN_FSYSNA_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Fsysna"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "fsysna" ascii wide nocase
        $s2 = "fsysna" ascii wide nocase
        $s3 = "trojan:win32/fsysna" ascii wide nocase
        $s4 = "trojan.win32.fsysna" ascii wide nocase
        $s5 = "win32/fsysna" ascii wide nocase
        $s6 = "trojan.win32.fsysna" ascii wide nocase
        $s7 = "fsysna loader" ascii wide nocase
        $s8 = "trojan:win32/fsysna.gen" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Fsysna (Trojan) Execution & Triage
id: 69a527a1-e3f7-5cf6-955f-f4caf318bfca
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Fsysna 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/fsysna
- 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.t1105
- attack.t1021_002
- attack.t1562_001
- attack.t1059_003
- 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: medium

rule MALWARE_WIN_FSYSNA_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Fsysna 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 = "fsysna" 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
}

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Isolate the endpoint from the network immediately to prevent Fsysna from successfully downloading and executing its secondary payloads.
2. Audit the Windows Task Scheduler and Registry Run keys to identify and remove the Fsysna persistence mechanisms.
3. Review firewall and proxy logs to identify the C2 domains Fsysna attempted to contact, and block them enterprise-wide.
4. Perform a full memory and disk scan with a reputable EDR solution to eradicate the dropped executables and injected processes.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not close an incident simply because the initial Fsysna dropper was quarantined; always verify if secondary payloads were downloaded.
2. Avoid relying solely on manual file deletion, as the injected processes will likely just recreate the dropped binaries.

References & External Analysis

• NHS Digital Cybersecurity Alert - Fsysna Malware Profile
• Microsoft Defender Threat Encyclopedia - Trojan:Win32/Fsysna
• Trend Micro Threat Encyclopedia - Trojan.Win32.FSYSNA
• Search "fsysna" on VirusTotal (External Analysis)
• Search "fsysna" on Any.Run (Sandbox Sandbox)
• Search "fsysna" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Lotoor
• Sz4Aaw
• Spamha
• Doser
• Cool_Remote_Control
• Emgfamt7Gjgi
• Driverdevelop
• Y3K_Rat

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/fsysna.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.