Stubrc
Table of Contents
Overview
StubRC (cataloged across security vendors and threat intelligence databases under signatures including Trojan-Dropper.MSIL.StubRC, Backdoor:Win32/Stubrc, and Trojan:MSIL/StubRC) is a malicious stub loader and dropper framework active since 2016. Often deployed as an initial access stage or payload decrypter for commodity RATs, botnets, and ransomware, StubRC embeds encrypted secondary binaries within its assembly resource sections (RCData / manifest resources). Upon launch, the stub extracts the embedded payload in memory, decrypts it using AES or RC4 routines, and performs process hollowing or RunPE injection into legitimate Windows binaries like svchost.exe or RegSvcs.exe to execute without touching disk.
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: Trojan-Dropper.Msil.Stubrc.A · Backdoor:Win32/Stubrc!Rfn
MITRE ATT&CK Techniques
This family has been observed using the following ATT&CK techniques: T1055.012 · T1027.002 · T1140 · T1105 · T1082
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):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-EDA | Executable Deobfuscation Analysis | Detect | T1027.002 | Deploy static entropy scanners and dynamic memory-unpacking heuristics to identify obfuscated and packed PE structures. |
D3-PHA | Process Hollowing Analysis | Detect | T1055.012 | Inspect unbacked executable memory regions (PAGE_EXECUTE_READWRITE) for replaced PE image headers inside legitimate host processes. |
D3-SDA | System Discovery Analysis | Detect | T1082 | Alert on rapid enumerations of systeminfo, hostname, and registry hardware trees in short intervals. |
D3-NTI | Network Traffic Inspection | Detect | T1105 | Inspect deep packet payloads for anomalous staging binaries and unauthorized egress protocols. |
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_STUBRC_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Stubrc"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "stubrc" ascii wide nocase
$s2 = "trojan-dropper.msil.stubrc" ascii wide nocase
$s3 = "backdoor:win32/stubrc" ascii wide nocase
$s4 = "trojan:msil/stubrc" ascii wide nocase
$s5 = "dropper.msil.stubrc" ascii wide nocase
$s6 = "win32/stubrc" 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 - Stubrc (Trojan Downloader) Execution & Triage
id: 72acb755-231e-5aeb-8814-520d8fcdfd05
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Stubrc 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/stubrc
- 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.t1055_012
- attack.t1027_002
- attack.t1140
- attack.t1105
- attack.t1082
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_STUBRC_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Stubrc 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 = "stubrc" 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 Security Intelligence - Trojan-Dropper:MSIL/StubRC
- Search "stubrc" on VirusTotal (External Analysis)
- Search "stubrc" on Any.Run (Sandbox Sandbox)
- Search "stubrc" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Trojan-Dropper.MSIL.StubRC?
StubRC is a .NET malicious stub loader and dropper framework that decrypts and executes embedded payloads in memory.
How does StubRC hide secondary malware payloads?
It stores encrypted payloads in compiled resource sections (RCData) and decrypts them dynamically during runtime.
What process injection techniques does StubRC utilize?
It utilizes process hollowing (RunPE) to inject decrypted payloads into legitimate binaries like svchost.exe or RegSvcs.exe.
Why is StubRC classified both as a dropper and a backdoor?
Because it drops full-featured backdoors and remote access trojans while sometimes retaining remote beaconing capability.
How can security teams defend against StubRC loaders?
Enforce behavioral monitoring on process hollowing, enable AMSI for .NET script inspection, and restrict unverified binaries.
How do I remove the Stubrc Trojan_Downloader from Windows?
Manual removal of Stubrc 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 Stubrc a virus or a Trojan_Downloader?
Stubrc is classified as a Trojan_Downloader. Unlike traditional viruses that infect files, modern malware like Stubrc typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Stubrc infection?
Symptoms of Stubrc 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 Stubrc 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/stubrc.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.