Bisonal

Overview

Bisonal (classified in antivirus detection telemetry under designations including Trojan:Win32/Bisonal, Trojan.Win32.Bisonal, and Win32/Bisonal) is a multi-stage trojan engineered to disguise itself as legitimate software, execute unauthorized commands, and coordinate with external command-and-control infrastructure. Disseminated across enterprise networks and consumer workstations via social engineering, phishing attachments, malicious drive-by downloads, or weaponized software cracks, Bisonal executes an initial reconnaissance phase upon system ingress. The binary evaluates host privileges, detects active hypervisors and sandbox environments to evade behavioral analysis, and establishes resilient autostart persistence by configuring registry keys under HKCU\Software\Microsoft\Windows\CurrentVersion\Run or registering background Windows services. Operational mechanics characteristic of this family include deceptive executable masquerading, registry run key autostart, system telemetry gathering, and remote C2 beaconing. Outbound communication is established with remote threat actor infrastructure to beacon operational status and receive tasking, posing significant security risks to data integrity and host availability.

Known aliases

Threat reports may refer to this family under multiple names:

• Trojan:Win32/Bisonal
• Trojan.Win32.Bisonal
• Win32/Bisonal

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: Restrict execution of scripting languages such as PowerShell, VBScript, or Python to authorized administrators. Enforce Script Block Logging.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

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_BISONAL_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Bisonal"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "bisonal" ascii wide nocase
        $s2 = "trojan:win32/bisonal" ascii wide nocase
        $s3 = "trojan.win32.bisonal" ascii wide nocase
        $s4 = "win32/bisonal" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Bisonal (Trojan) Execution & Triage
id: 16574625-a59d-5292-87df-2538e0230bfe
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Bisonal 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/bisonal
- 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.t1059_003
- attack.t1027
- attack.t1547_001
- attack.t1071_001
- attack.t1105
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: medium

rule MALWARE_WIN_BISONAL_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Bisonal 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 = "bisonal" 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. Immediately isolate the compromised endpoint and assume the entire domain is compromised; engage a specialized Incident Response (IR) firm.
2. Perform a comprehensive enterprise-wide hunt for similar malware, focusing on the specific C2 infrastructure identified on the initial host.
3. Initiate a full credential reset for the entire organization, as the attackers likely deployed tools like Mimikatz after establishing the backdoor.
4. Analyze email gateways and proxy logs to identify the original spear-phishing email and determine if other employees were targeted or compromised.

What to Avoid

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

1. Do not attempt to remediate an APT infection by simply deleting the Bisonal executable; the actors almost certainly have secondary backdoors deployed.
2. Avoid communicating about the incident on the compromised corporate network; assume the attackers are monitoring emails.

References & External Analysis

• Microsoft Defender Threat Encyclopedia - Trojan:Win32/Bisonal
• Kaspersky Threat Intelligence - Trojan.Win32.Bisonal
• MITRE ATT&CK - Enterprise Techniques
• Search "bisonal" on VirusTotal (External Analysis)
• Search "bisonal" on Any.Run (Sandbox Sandbox)
• Search "bisonal" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Adgazelle
• Zpevdo
• Karamanak
• Krepper
• Streespyer
• Bandoo
• Remexi
• Rkit

Machine-readable

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