Yelloader
Table of Contents
Overview
Yelloader (tracked across security intelligence catalogs under signatures including TrojanDownloader:Win32/Yelloader, Trojan:Win32/Yelloader, and Trojan.Yelloader) is an evasive modular trojan downloader and stager active since 2016. Infiltrating endpoints primarily through malicious email attachments and weaponized installers, Yelloader uses anti-analysis techniques including hypervisor detection and delayed execution to bypass sandboxes. It establishes persistence via Windows Registry Run keys, beacons out to C2 servers over HTTPS, and downloads encrypted secondary binary payloads dropped into %Temp% or hollowed into trusted system 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/Yelloader.A · Trojandownloader:Win32/Yelloader.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_YELLOADER_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Yelloader"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "yelloader" ascii wide nocase
$s2 = "trojandownloader:win32/yelloader" ascii wide nocase
$s3 = "trojan:win32/yelloader" ascii wide nocase
$s4 = "trojan.yelloader" ascii wide nocase
$s5 = "win32/yelloader" ascii wide nocase
$s6 = "trojandownloader:win32/yelloader.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 - Yelloader (Trojan Downloader) Execution & Triage
id: da7fe249-ebc0-5d9b-8a68-e09fdb12da28
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Yelloader 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/yelloader
- 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_YELLOADER_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Yelloader 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 = "yelloader" 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
Frequently Asked Questions
What is TrojanDownloader:Win32/Yelloader?
Yelloader is an evasive trojan downloader that stages secondary malware payloads like ransomware and infostealers onto Windows systems.
How does Yelloader bypass sandbox analysis?
It checks for hypervisor artifacts, virtual machine drivers, and delays execution using sleep calls to exceed sandbox timeouts.
What secondary payloads are dropped by Yelloader?
Threat actors use Yelloader to deploy banking trojans, cryptocurrency stealers, keyloggers, and ransomware.
How does Yelloader maintain persistence on the system?
It writes autostart entries in HKCU\Software\Microsoft\Windows\CurrentVersion\Run and creates scheduled tasks.
What defensive steps prevent Yelloader compromise?
Enforce email gateway attachment filtering, restrict executable execution in %Temp%, and deploy modern behavioral EDR.
How do I remove the Yelloader Trojan_Downloader from Windows?
Manual removal of Yelloader 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 Yelloader a virus or a Trojan_Downloader?
Yelloader is classified as a Trojan_Downloader. Unlike traditional viruses that infect files, modern malware like Yelloader typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Yelloader infection?
Symptoms of Yelloader 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 Yelloader 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/yelloader.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.