{
  "family": "bsdownloader",
  "sample_count": 1,
  "category": "trojan_downloader",
  "description": "Bsdownloader (classified in antivirus detection telemetry under designations including TrojanDownloader:Win32/Bsdownloader, TrojanDownloader.Win32.Bsdownloader, and Win32/Bsdownloader) is a stealthy staging trojan engineered to establish host persistence and download secondary crimeware payloads onto compromised endpoints. Disseminated across enterprise networks and consumer workstations via social engineering, phishing attachments, malicious drive-by downloads, or weaponized software cracks, Bsdownloader 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 sandbox evasion, staging directory payload extraction, autostart registry configuration, and encrypted HTTP/HTTPS payload delivery. 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.",
  "cta": "Published by the SystemHelpdesk Threat Intelligence Team.",
  "aliases": [
    "TrojanDownloader:Win32/Bsdownloader",
    "TrojanDownloader.Win32.Bsdownloader",
    "Win32/Bsdownloader"
  ],
  "enrichment_level": "curated_sourced",
  "faq": [
    {
      "@type": "Question",
      "name": "What is TrojanDownloader:Win32/Bsdownloader?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Bsdownloader is a trojan downloader threat designed to infiltrate Windows systems and execute unauthorized operations without user consent."
      }
    },
    {
      "@type": "Question",
      "name": "How does Bsdownloader compromise target systems?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "It commonly infiltrates systems via phishing emails, trojanized software installers, exploit kits, or unpatched vulnerabilities."
      }
    },
    {
      "@type": "Question",
      "name": "What persistence mechanisms does Bsdownloader utilize?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "It typically creates autostart entries in the Windows Registry (HKCU/HKLM Run keys), registers scheduled tasks, or installs hidden background services."
      }
    },
    {
      "@type": "Question",
      "name": "What risks does Bsdownloader pose to an enterprise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "It can lead to credential theft, system manipulation, unauthorized remote access, data loss, or secondary malware delivery."
      }
    },
    {
      "@type": "Question",
      "name": "How can administrators detect and eliminate Bsdownloader?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Deploy modern EDR solutions with updated behavioral signatures, isolate infected endpoints, audit autostart persistence entries, and conduct full antimalware scans."
      }
    }
  ],
  "faq_count": 5,
  "mitre_attack": [
    "T1105",
    "T1059.001",
    "T1547.001",
    "T1071.001",
    "T1082"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-10-16",
  "mitre_attack_detail": [
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer (The core function of fetching the secondary payload)",
      "tactic": "Command and Control"
    },
    {
      "id": "T1055",
      "name": "Process Injection (Injecting into svchost.exe to hide network traffic)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1566.001",
      "name": "Phishing: Spearphishing Attachment (Primary distribution vector)",
      "tactic": "Initial Access"
    },
    {
      "id": "T1027",
      "name": "Obfuscated Files or Information (Packing the downloader to bypass AV)",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Isolate the endpoint immediately; if Bsdownloader is detected, you must assume it is actively attempting to download a worse payload.",
    "Analyze EDR and proxy logs to identify the C2 domains Bsdownloader contacted, and block those domains enterprise-wide.",
    "Determine if the secondary payload was successfully downloaded and executed; if so, shift response efforts to containing the final payload (e.g., ransomware).",
    "Hunt for the specific spearphishing email that delivered Bsdownloader and purge it from all user inboxes."
  ],
  "what_to_avoid": [
    "Do not close the incident simply because the AV quarantined the Bsdownloader executable; you must verify network logs to ensure the payload wasn't already downloaded.",
    "Avoid relying solely on static AV signatures, as downloaders are frequently repacked."
  ],
  "target_industries": [
    "Healthcare",
    "Critical Infrastructure",
    "Enterprise"
  ],
  "motivation": "Financial Extortion",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ],
  "attack_stage": [
    "defense_evasion",
    "impact"
  ],
  "ecosystem": [
    "windows_pe"
  ],
  "is_emerging": false,
  "sources": [
    {
      "name": "Microsoft Defender Threat Encyclopedia - TrojanDownloader:Win32/Bsdownloader",
      "url": "https://www.microsoft.com/en-us/wdsi/threats/malware-encyclopedia-description?Name=TrojanDownloader:Win32/Bsdownloader"
    },
    {
      "name": "Kaspersky Threat Intelligence - TrojanDownloader.Win32.Bsdownloader",
      "url": "https://threats.kaspersky.com/en/threat/"
    },
    {
      "name": "MITRE ATT&CK - Enterprise Techniques",
      "url": "https://attack.mitre.org/techniques/T1105/"
    }
  ],
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows 7"
  ]
}