Subti
Table of Contents
Overview
Subti (classified across threat telemetry and antivirus databases as TrojanDownloader:Win32/Subti, Trojan:Win32/Subti, and Win32/Subti) is an evasive multi-stage Windows trojan downloader active since 2016. Often distributed through spam emails containing password-protected archive files or deceptive download wrappers on file-sharing sites, Subti specializes in staging secondary crimeware threats onto compromised endpoints. Upon execution, Subti conducts environmental anti-sandbox checks (evaluating system uptime, cursor coordinates, and screen resolution) before establishing outbound HTTP/HTTPS connections to attacker-controlled distribution nodes. It downloads encrypted secondary binary blobs, decrypts them in memory using multi-byte XOR keys, and drops or injects payloads—frequently cryptocurrency miners, modular infostealers, or ransomware loaders—directly into Windows user processes.
Known aliases
Threat reports may refer to this family under multiple names:
Family Pedigree & Lineage
Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:
Known Derivatives & Downstream Variants: Trojandownloader:Win32/Subti.A · Trojandownloader:Win32/Subti.B
MITRE ATT&CK Techniques
This family has been observed using the following ATT&CK techniques: T1105 · T1497.001 · T1055 · T1071.001 · T1547.001
Tactical Mitigations
Based on the techniques used by this family, consider the following defensive strategies:
- T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.
- 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):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-PIAD | Process Injection Analysis & Detection | Detect | T1055 | Monitor cross-process thread creation (CreateRemoteThread) and asynchronous procedure calls (QueueUserAPC). |
D3-WAF | Web Content Filtering & Inspection | Filter | T1071.001 | Block newly registered domains (NRDs) and inspect HTTP Host and URI headers for known C2 profiles. |
D3-NTI | Network Traffic Inspection | Detect | T1105 | Inspect deep packet payloads for anomalous staging binaries and unauthorized egress protocols. |
D3-EED | Execution Environment Detection | Detect | T1497.001 | Configure malware sandboxes to emulate legitimate hardware metrics, realistic mouse movements, and valid system uptimes. |
D3-RPM | Registry Persistence Monitoring | Detect | T1547.001 | Audit and restrict write privileges to user and machine-level Registry Run/RunOnce keys using Endpoint Privilege Management. |
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:
Tier 1 Primitive Artifact Rule (Fast Triage)
Matches raw strings and file markers. Vulnerable to binary repacking and simple obfuscation.
rule MALWARE_WIN_SUBTI_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Subti"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "subti" ascii wide nocase
$s2 = "trojandownloader:win32/subti" ascii wide nocase
$s3 = "trojan:win32/subti" ascii wide nocase
$s4 = "trojan.subti" ascii wide nocase
$s5 = "win32/subti" ascii wide nocase
$s6 = "trojandownloader:win32/subti.a" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Tier 2 Behavioral Context Rule (Process Chains & Sigma)
Tracks parent-child process anomalies and suspicious scripting telemetry. Resilient against file renames.
title: SystemHelpDesk Detection - Subti (Trojan Downloader) Execution & Triage
id: 98c95914-de72-58c6-9c9a-a83723623b66
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Subti 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/subti
- 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.t1497_001
- attack.t1055
- attack.t1071_001
- 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: mediumTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_SUBTI_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Subti 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 = "subti" 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
}References & External Analysis
- Microsoft Defender Threat Encyclopedia - TrojanDownloader:Win32/Subti
- Trend Micro Threat Encyclopedia - Trojan.Win32.Subti
- Search "subti" on VirusTotal (External Analysis)
- Search "subti" on Any.Run (Sandbox Sandbox)
- Search "subti" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is TrojanDownloader:Win32/Subti?
Subti is a stealthy Windows trojan downloader designed to bypass sandbox analysis and download secondary malware payloads onto infected hosts.
How does Subti detect virtualized sandboxes?
It measures elapsed system uptime, verifies human mouse cursor movements across consecutive API queries, and checks screen resolutions.
What payloads are typically downloaded by Subti?
Operators utilize Subti to deliver cryptocurrency miners, modular infostealers, banking trojans, and ransomware.
How does Subti conceal downloaded binary payloads?
Payloads are retrieved in encrypted formats masked as PNG or JPG image files, and decrypted in memory using multi-byte XOR algorithms.
How can systems be defended against Subti downloaders?
Block executable launches from temporary directories (%Temp%, %AppData%), deploy behavioral EDR monitoring, and inspect encrypted network streams.
How do I remove the Subti Trojan_Downloader from Windows?
Manual removal of Subti is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.
Is Subti a virus or a Trojan_Downloader?
Subti is classified as a Trojan_Downloader. Unlike traditional viruses that infect files, modern malware like Subti typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Subti infection?
Symptoms of Subti can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.
Protect Your Network Against Trojan_Downloaders
Want to prevent Subti and similar threats from compromising your organization? Read our comprehensive defensive guide: Banking Trojan Protection for Businesses.
📣 Threat Intel Correction or Update?
Notice an outdated IOC, unlisted alias, or disputed attribution? Threat researchers are invited to propose an update on GitHub or contact the SystemHelpDesk research desk. All community revisions are credited in our public CHANGELOG.
Machine-readable
Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/subti.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.