Sysn

Overview

Sysn (cataloged across security intelligence as Trojan:Win32/Sysn, Trojan.Win32.Sysna, and Swisyn) is a resilient family of Delphi-based Windows trojans and payload loaders active since 2011. Characterized by aggressive defense evasion and system modification capabilities, Sysn is distributed via weaponized spearphishing attachments, trojanized key generators, and drive-by web exploit kits. Upon execution on a compromised endpoint, Sysn deploys dynamic API hashing and multi-layered binary packing to evade static signature detection. It systematically impairs host security controls: modifying the Windows Registry to disable the Windows Firewall (DisableFirewall), terminating security monitoring services, and altering the local HOSTS file (C:\Windows\System32\drivers\etc\hosts) to redirect antivirus update domains and security vendor websites to loopback (127.0.0.1). Sysn establishes persistence by installing a rogue Windows Service (T1543.003) or modifying Registry Run keys, subsequently initiating encrypted HTTP beaconing to command-and-control servers to download and execute secondary malware payloads including information stealers and banking trojans.

Known aliases

Threat reports may refer to this family under multiple names:

• Trojan:Win32/Sysn
• Trojan.Win32.Sysn
• Trojan.Win32.Sysna
• Swisyn
• Win32/Sysn

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: Delphi Trojan Dropper Families

Known Derivatives & Downstream Variants: Sysn.A · Sysna.B · Swisyn Loader

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.

• 8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b
• 9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c

Delivery vectors

• Malicious email attachments disguised as business invoices
• Trojanized utility keygens and software cracks

Persistence mechanisms

• Rogue Windows Service in HKLM\SYSTEM\CurrentControlSet\Services
• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SysnManager

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_SYSN_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Sysn"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "sysn" ascii wide nocase
        $s2 = "trojan:win32/sysn" ascii wide nocase
        $s3 = "trojan.win32.sysn" ascii wide nocase
        $s4 = "trojan.win32.sysna" ascii wide nocase
        $s5 = "swisyn" ascii wide nocase
        $s6 = "win32/sysn" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Sysn (Trojan) Execution & Triage
id: e5d43bb9-a9df-5fcf-af7b-b8bcef3247d9
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Sysn 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/sysn
- 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.t1543_003
- attack.t1562_001
- attack.t1112
- attack.t1562_004
- 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_SYSN_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Sysn 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 = "sysn" 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. Immediately isolate the compromised endpoint from the network to halt C2 communications and secondary malware downloads.
2. Audit the Windows HOSTS file (C:\Windows\System32\drivers\etc\hosts) and remove malicious entries blocking security vendor domains.
3. Re-enable and reset Windows Firewall policies using 'netsh advfirewall reset' to restore network boundary defenses.
4. Audit Windows Services using 'sc.exe' and Registry Run keys to identify and delete rogue Sysn service registrations.

What to Avoid

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

1. Do not trust local endpoint security alerts during triage, as Sysn is specifically designed to tamper with native security logging.
2. Avoid relying solely on automated file deletion without inspecting the modified system services and firewall configurations.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Trojan:Win32/Sysn
• Kaspersky Threat Intelligence - Trojan.Win32.Sysna
• Search "sysn" on VirusTotal (External Analysis)
• Search "sysn" on Any.Run (Sandbox Sandbox)
• Search "sysn" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Pcreviver
• Faketool
• Injeber
• Infector_Ng_2004
• Zpevdo
• Disfa
• Njlogger
• Favadd

Machine-readable

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