Siscos
Table of Contents
Overview
Siscos (cataloged across security vendors and threat intelligence databases under signatures including Trojan:Win32/Siscos, Trojan.Win32.Siscos, and Win32/Siscos) is a stealthy Windows trojan and payload delivery stager active since 2017. Distributed through bundled software installers, cracked utilities, and malicious email links, Siscos executes multi-stage compromise routines on target endpoints. Upon launch, the malware performs host profiling, drops randomized payloads into %LocalAppData%\Temp, and establishes startup persistence via Windows Registry Run keys. Once established, Siscos initiates encrypted HTTP/TCP communications with command-and-control servers, enabling remote operators to deploy secondary malware payloads such as ransomware, banking trojans, and credential stealers.
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:Win32/Siscos.A · Trojan:Win32/Siscos!Rfn
MITRE ATT&CK Techniques
This family has been observed using the following ATT&CK techniques: T1105 · T1547.001 · T1071.001 · T1082 · T1027
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-BDA | Binary De-obfuscation & Unpacking | Analyze | T1027 | Utilize memory dump scanners and entropy inspection to unpack encrypted stagers during process creation. |
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-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. |
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_SISCOS_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Siscos"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "siscos" ascii wide nocase
$s2 = "trojan:win32/siscos" ascii wide nocase
$s3 = "trojan.win32.siscos" ascii wide nocase
$s4 = "win32/siscos" ascii wide nocase
$s5 = "trojan:win32/siscos!rfn" ascii wide nocase
$s6 = "siscos stager" 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 - Siscos (Trojan) Execution & Triage
id: 189f0e48-ba08-5c15-ae3f-83c65fa39917
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Siscos 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/siscos
- https://malware-families-catalog.systemhelpdesk.com/defensive/downloader-dropper-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
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1105
- attack.t1547_001
- attack.t1071_001
- attack.t1082
- 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: mediumTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_SISCOS_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Siscos 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 = "siscos" 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 - Trojan:Win32/Siscos
- Search "siscos" on VirusTotal (External Analysis)
- Search "siscos" on Any.Run (Sandbox Sandbox)
- Search "siscos" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is Trojan:Win32/Siscos?
Siscos is a stealthy Windows trojan and initial access stager designed to deliver secondary malicious payloads.
How does Siscos infect Windows computers?
It commonly infiltrates systems via freeware software bundlers, pirated application patches, and phishing links.
Where does Siscos drop its execution artifacts?
It unpacks randomized binaries and staging files into user %LocalAppData%\Temp directories.
What secondary threats are delivered by Siscos?
It delivers high-severity payloads including ransomware, information stealers, and banking trojans.
How can defenders clean a Siscos infection?
Run a Microsoft Defender Offline scan, clean the %LocalAppData%\Temp folder, and remove rogue Registry Run keys.
How do I remove the Siscos Trojan from Windows?
Manual removal of Siscos 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 Siscos a virus or a Trojan?
Siscos is classified as a Trojan. Unlike traditional viruses that infect files, modern malware like Siscos typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Siscos infection?
Symptoms of Siscos 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 Trojans
Want to prevent Siscos 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/siscos.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.