Mofksys

Overview

Mofksys (classified as Worm:Win32/Mofksys across Microsoft Defender, Sophos, and Kaspersky) is an evasive network and removable drive worm targeting Windows systems. Mofksys spreads by copying itself to root directories of connected USB flash drives and external hard drives along with weaponized autorun.inf files or masqueraded LNK shortcut files. Once launched on a victim endpoint, Mofksys deploys Managed Object Format (MOF) files (.mof) and Windows Management Instrumentation (WMI) event subscriptions to achieve high-privilege persistent execution. Mofksys disables security monitoring tools, creates backdoors, and connects to remote command-and-control servers to download follow-on malicious payloads.

Known aliases

Threat reports may refer to this family under multiple names:

• Worm:Win32/Mofksys
• Trojan:Win32/Mofksys
• Win32/Mofksys
• Mofksys Worm
• Worm.Mofksys

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):

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_MOFKSYS_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Mofksys"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "mofksys" ascii wide nocase
        $s2 = "worm:win32/mofksys" ascii wide nocase
        $s3 = "trojan:win32/mofksys" ascii wide nocase
        $s4 = "win32/mofksys" ascii wide nocase
        $s5 = "mofksys worm" ascii wide nocase
        $s6 = "worm.mofksys" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Mofksys (Worm) Execution & Triage
id: a762997d-8182-5a8b-9c85-26b68f3e188b
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Mofksys 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/mofksys
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-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.worm
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1091
- attack.t1546_003
- attack.t1047
- attack.t1547_001
- attack.t1105
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_MOFKSYS_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Mofksys 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 = "mofksys" 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. Disconnect the infected machine from the local network and internet immediately to halt the worm's lateral movement and data exfiltration.
2. Disable AutoRun/AutoPlay across the organization to prevent the worm from executing via infected USB drives.
3. Perform a full system scan with an updated enterprise antivirus solution, booting into Safe Mode if necessary to bypass active rootkits.
4. Change all user credentials and administrative passwords that were stored or used on the infected system, as they may have been compromised.

What to Avoid

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

1. Do not connect any USB drives or external storage to the infected system until it has been completely sanitized.
2. Do not assume only one machine is infected; worms spread rapidly, so you must sweep the entire network for IoCs.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Worm:Win32/Mofksys
• Sophos Threat Center - Worm_Mofksys Analysis
• MITRE ATT&CK - Event Triggered Execution: WMI Event Subscription (T1546.003)
• Search "mofksys" on VirusTotal (External Analysis)
• Search "mofksys" on Any.Run (Sandbox Sandbox)
• Search "mofksys" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Worm)

Explore other documented threats in the same operational category:

• Hworld
• Brontok
• Mabezat
• Blasterx
• Warezov
• Pykspa
• Cambot
• Chir

Machine-readable

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