Nymeria

Overview

Nymeria (cataloged across security vendors as TrojanDownloader:Win32/Nymeria, Trojan.Nymeria, and Backdoor:Win32/Nymeria) is a modular Windows trojan downloader and reconnaissance threat active since 2016. Often observed acting as a multi-stage loader or dropper in campaigns delivering commercial remote access tools (such as LodaRAT) and credential stealers, Nymeria infiltrates endpoints through malicious spearphishing email attachments, weaponized Office macro documents, and trojanized freeware downloads. Upon initial execution, Nymeria drops a copy of its executable stub into hidden user directories (such as %LocalAppData%\Temp or %AppData%) and establishes persistence via Windows Registry Run keys and scheduled tasks. The malware deploys in-memory anti-debugging and virtual machine detection routines to verify that it is running in a live user environment rather than an analysis sandbox. Once cleared, Nymeria captures system reconnaissance data (hostname, user privilege level, OS architecture) and initiates encrypted HTTP/HTTPS beaconing to remote command-and-control servers to download, unpack, and launch secondary payloads including info-stealers, keyloggers, and banking trojans.

Known aliases

Threat reports may refer to this family under multiple names:

• TrojanDownloader:Win32/Nymeria
• Trojan.Nymeria
• Win32/Nymeria
• Backdoor:Win32/Nymeria

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: Modular Windows Downloader Trojans

Known Derivatives & Downstream Variants: Nymeria.A · Nymeria Loader V2

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.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

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.

• 2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2a3b
• 3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a7b8c9d0e1f2a3b4c

Delivery vectors

• Malicious email attachments disguised as invoices or receipts
• Deceptive software downloads from third-party distribution portals

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\NymeriaUpdate
• Scheduled Task executing dropped loader from %LocalAppData%\Temp

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_NYMERIA_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Nymeria"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "nymeria" ascii wide nocase
        $s2 = "trojandownloader:win32/nymeria" ascii wide nocase
        $s3 = "trojan.nymeria" ascii wide nocase
        $s4 = "win32/nymeria" ascii wide nocase
        $s5 = "backdoor:win32/nymeria" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Nymeria (Downloader) Execution & Triage
id: bf4a1235-748f-5a43-ae13-720f115e1020
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Nymeria 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/nymeria
- 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.downloader
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1105
- attack.t1566_001
- attack.t1055
- attack.t1547_001
- attack.t1027
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_NYMERIA_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Nymeria 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 = "nymeria" 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 internal networks to prevent secondary malware staging and credential exfiltration.
2. Capture a volatile memory image to preserve injected downloader threads, active socket connections, and decrypted C2 domains.
3. Inspect the Windows Task Scheduler and Registry Run keys to eliminate persistent autostart entries referencing %Temp% binaries.
4. Audit all corporate user accounts authenticated on the endpoint and enforce immediate password resets.

What to Avoid

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

1. Do not close the incident merely because the initial Nymeria file was quarantined; always verify if secondary payloads executed.
2. Avoid allowing non-whitelisted executable binaries to run directly from the Windows %Temp% and %AppData% directories.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - TrojanDownloader:Win32/Nymeria
• PCRisk Threat Research - Trojan.Nymeria Analysis
• Search "nymeria" on VirusTotal (External Analysis)
• Search "nymeria" on Any.Run (Sandbox Sandbox)
• Search "nymeria" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Downloader)

Explore other documented threats in the same operational category:

• Banload
• Dofoil
• Reconyc
• Dlhelper
• Fraudrop
• Aim_Downloader
• Gepys
• Tinyloader

Machine-readable

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