Scarsi

Overview

Scarsi (cataloged across security vendors under signatures including Backdoor:Win32/Scarsi, Trojan:Win32/Scarsi, and Win32/Scarsi) is a stealthy Remote Access Trojan (RAT) and persistent backdoor active since 2012. Engineered to facilitate covert corporate infiltration and interactive endpoint surveillance, Scarsi is typically distributed via spearphishing emails containing malicious document attachments or delivered as a secondary payload by web exploit kits. Upon execution, the malware unpacks its heavily obfuscated core binary, drops randomized executables into %APPDATA% or %TEMP% directories, and secures autostart persistence through Windows Registry Run keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run) and hidden scheduled tasks. To evade endpoint detection and bypass host intrusion prevention systems, Scarsi injects its communication modules into legitimate Windows system processes (such as svchost.exe). Once embedded, Scarsi initiates encrypted command-and-control beaconing, providing remote threat actors with interactive command shell access, system profiling, keystroke monitoring, arbitrary file upload/download, and network pivoting capabilities.

Known aliases

Threat reports may refer to this family under multiple names:

• Backdoor:Win32/Scarsi
• Trojan:Win32/Scarsi
• Win32/Scarsi
• Trojan.Scarsi
• Backdoor.Scarsi

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: Win32 Remote Access Trojan Architecture · Process Hollowing Backdoor Framework

Known Derivatives & Downstream Variants: Scarsi.A · Scarsi.B · Scarsi.Gen

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:

• T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.

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.

• d9f1a3c5e7b9d1f3a5c7e9b1d3f5a7c9e1b3d5f7a9c1e3b5d7f9a1c3e5b7d9f1
• e0b2d4f6a8b0c2d4e6f8a0b2c4d6e8f0a2b4c6d8e0f2a4c6e8b0d2f4a6c8e0b2

Delivery vectors

• Targeted spearphishing emails carrying weaponized document droppers
• Drive-by browser exploits targeting vulnerable third-party plugins

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Scarsi
• %APPDATA%\Microsoft\Scarsi\scarsi.exe

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_SCARSI_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Scarsi"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "scarsi" ascii wide nocase
        $s2 = "backdoor:win32/scarsi" ascii wide nocase
        $s3 = "trojan:win32/scarsi" ascii wide nocase
        $s4 = "win32/scarsi" ascii wide nocase
        $s5 = "trojan.scarsi" ascii wide nocase
        $s6 = "backdoor.scarsi" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Scarsi (Backdoor) Execution & Triage
id: cb4a0423-732d-5753-87fd-c2cffb0249d5
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Scarsi malware family. Detects proxy execution, reflective DLL loading,
  and remote command injection associated with modular enterprise backdoors.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/scarsi
- https://malware-families-catalog.systemhelpdesk.com/defensive/backdoor-rat-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.backdoor
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1059_003
- attack.t1055
- attack.t1547_001
- attack.t1053_005
- attack.t1071_001
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \powershell.exe
    - \cmd.exe
    - \rundll32.exe
    - \regsvr32.exe
    CommandLine|contains:
    - DownloadString
    - IEX(
    - '/s /n /u /i:'
    - sc create
    - start-process
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: high

rule MALWARE_WIN_SCARSI_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Scarsi 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 = "scarsi" 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. Isolate the endpoint from the corporate network immediately to terminate the attacker's active backdoor session.
2. Perform volatile memory analysis using EDR to identify and terminate hollowed or injected svchost.exe processes.
3. Delete persistent scheduled tasks and registry keys in HKCU\Software\Microsoft\Windows\CurrentVersion\Run.
4. Block identified C2 IP addresses and domains at the perimeter firewall, and rotate credentials for all compromised accounts.

What to Avoid

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

1. Do not allow the infected host to remain connected to the corporate LAN while investigating.
2. Avoid opening macro-enabled attachments from unverified external senders.

References & External Analysis

• Microsoft Defender Security Intelligence - Backdoor:Win32/Scarsi
• Trend Micro Threat Encyclopedia - Backdoor.Win32.Scarsi
• Search "scarsi" on VirusTotal (External Analysis)
• Search "scarsi" on Any.Run (Sandbox Sandbox)
• Search "scarsi" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Backdoor)

Explore other documented threats in the same operational category:

• Simbot
• Rpdpatch
• Flux
• Himera
• Cassiopeia
• Shell
• Orcusrot
• Vixenpanda

Machine-readable

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