Winloadsda

Overview

WinloadSDA (classified across security vendors as TrojanDownloader:Win32/WinloadSDA and Trojan:Win32/WinloadSDA) is an evasive trojan downloader and stager that masquerades as genuine Windows boot and system loader files (such as winload.exe). Distributed through compromised software downloads and exploit kits, WinloadSDA executes stealth sandbox evasion checks before establishing persistence under HKCU\Software\Microsoft\Windows\CurrentVersion\Run. It connects via encrypted HTTPS POST requests to remote command-and-control servers, transmitting endpoint hardware identifiers and downloading secondary malicious payloads, including banking trojans, infostealers, and commodity ransomware.

Known aliases

Threat reports may refer to this family under multiple names:

• TrojanDownloader:Win32/WinloadSDA
• Trojan:Win32/WinloadSDA
• Win32/WinloadSDA
• WinloadSDA Loader
• WinloadSDA Trojan

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_WINLOADSDA_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Winloadsda"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "winloadsda" ascii wide nocase
        $s2 = "trojandownloader:win32/winloadsda" ascii wide nocase
        $s3 = "trojan:win32/winloadsda" ascii wide nocase
        $s4 = "win32/winloadsda" ascii wide nocase
        $s5 = "winloadsda loader" ascii wide nocase
        $s6 = "winloadsda trojan" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Winloadsda (Trojan Downloader) Execution & Triage
id: fa3e5c6f-3dda-5159-a818-d2d1e4ec9593
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Winloadsda 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/winloadsda
- 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.trojan-downloader
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1105
- attack.t1036_005
- attack.t1547_001
- attack.t1053_005
- attack.t1071_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_WINLOADSDA_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Winloadsda 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 = "winloadsda" 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. Quarantine the endpoint to halt the active exfiltration of browsing telemetry and the downloading of further adware modules.
2. Audit Windows Group Policies and the Registry to remove any forced extension installation policies created by the adware.
3. Deploy an enterprise adware removal tool (e.g., AdwCleaner) to locate and strip the deeply embedded registry hooks and watchdog services.
4. Force a complete reset of all installed web browsers to factory defaults to eradicate the rogue extensions and restore the homepage.

What to Avoid

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

1. Do not rely solely on the browser's 'remove extension' button; Winloadsda frequently uses GPOs and watchdog services to immediately reinstall itself.
2. Avoid ignoring the infection; adware tracking data is highly detailed and may expose corporate activities or access to internal portals.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - TrojanDownloader:Win32/WinloadSDA
• Trend Micro Threat Encyclopedia - Trojan.Win32.WinloadSDA
• MITRE ATT&CK - Masquerading: Match Legitimate Name or Location (T1036.005)
• Search "winloadsda" on VirusTotal (External Analysis)
• Search "winloadsda" on Any.Run (Sandbox Sandbox)
• Search "winloadsda" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan Downloader)

Explore other documented threats in the same operational category:

• Subti
• Stubrc
• Bundleloader
• Centrumdownloader
• Nsismod
• Zippyloader
• Scrop
• Slugin

Machine-readable

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