{
  "family": "slenfbot",
  "sample_count": 2,
  "category": "advanced_threat",
  "description": "Worm:Win32/Slenfbot is a highly infectious network worm and botnet agent notorious for its aggressive self-propagation methods. Once executed on a host, it immediately attempts to replicate itself across the local network and to any connected removable media (USB drives), while simultaneously connecting the infected machine to a central IRC-based Command and Control (C2) botnet for further instructions, such as launching DDoS attacks or downloading additional malware.<br><br><b>Understanding Slenfbot (USB Worms/Botnets)</b><br>To an end-user, the infection might be unnoticeable until their network connection slows to a crawl due to DDoS activity or aggressive scanning. For a security administrator, a Slenfbot outbreak is a severe incident that can rapidly paralyze a corporate network. It exploits the human tendency to share files via USB (`T1091`) and weak network share permissions (`T1021.002`).<br><br><b>Execution and Propagation Mechanics</b><br>Slenfbot is most commonly introduced into an environment via an infected USB drive. It relies on the Windows `autorun.inf` feature (or tricks the user into clicking a disguised executable) to launch (`T1204.002`). Upon execution, it copies itself to the Windows system folder and establishes persistence via the Registry Run keys. Crucially, it immediately begins polling for new USB drives; when one is inserted, it silently copies itself and a malicious `autorun.inf` to the drive. Simultaneously, it connects to an IRC server (`T1071.002`) to join the botnet, awaiting commands from the botmaster.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is rapid, widespread infection and potential involvement in coordinated botnet attacks. Host-based IoCs include the presence of malicious `.exe` or `.vbs` files and hidden `autorun.inf` files on the root directory of all attached USB drives. EDR will detect the creation of autostart registry keys pointing to executables in the `System32` directory. Network IoCs are highly visible: unauthorized IRC traffic (often TCP ports 6667-6669) connecting to unknown domains, and massive internal network scanning (SMB/Port 445) as the worm attempts lateral movement.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Slenfbot and what threat category does it belong to?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Slenfbot is classified as a Advanced Threat. Documented across security telemetry, it is engineered to execute unauthorized operations, establish persistent footholds on target endpoints, and facilitate malicious campaigns targeting enterprise and individual environments."
      }
    },
    {
      "@type": "Question",
      "name": "How does Slenfbot establish persistence and evade defensive controls?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Slenfbot typically establishes persistence through registry run keys, scheduled tasks, or service installations, while evading signature-based antivirus solutions through code obfuscation, memory injection, or anti-analysis sandbox checks."
      }
    },
    {
      "@type": "Question",
      "name": "What are the essential incident response steps for mitigating a Slenfbot compromise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Security teams responding to Slenfbot should immediately isolate affected endpoints from the network, perform memory triage to capture volatile forensic artifacts, audit registry and startup persistence mechanisms, revoke exposed user credentials, and restore systems from verified, clean backups."
      }
    },
    {
      "@type": "Question",
      "name": "What lateral movement and credential access tactics does Slenfbot leverage in enterprise intrusions?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Slenfbot frequently utilizes privileged account harvesting techniques such as LSASS memory dumping, Kerberoasting, and token impersonation to escalate privileges. Once administrative credentials are acquired, it pivots across the victim network utilizing living-off-the-land binaries (LOLBins) such as WMI, PowerShell remoting, and PsExec, or abuses remote desktop protocols (RDP) to reach critical internal repositories and domain controllers."
      }
    },
    {
      "@type": "Question",
      "name": "How does Slenfbot maintain covert communications and evade perimeter network monitoring?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Slenfbot often relies on multi-stage command and control (C2) architectures utilizing encrypted protocols over standard web ports (HTTPS/443 or DNS tunneling) to blend in with legitimate enterprise network traffic. Many variants incorporate proxy networks, domain fronting, or cloud services (such as Microsoft Graph API, Google Drive, or Telegram) to masquerade C2 channels, bypassing traditional signature-based egress filtering."
      }
    }
  ],
  "faq_count": 5,
  "mitre_attack": [
    "T1091",
    "T1071.002",
    "T1547.001"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1091",
      "name": "Replication Through Removable Media (USB spreading)",
      "tactic": "Lateral Movement"
    },
    {
      "id": "T1071.002",
      "name": "Application Layer Protocol: File Transfer Protocols (IRC C2 communication)",
      "tactic": "Command and Control"
    },
    {
      "id": "T1547.001",
      "name": "Boot or Logon Autostart Execution (Registry persistence)",
      "tactic": "Persistence"
    }
  ],
  "containment_steps": [
    "Immediately disable the 'Autorun' and 'Autoplay' features across the entire enterprise via Group Policy to halt USB-based propagation.",
    "Isolate infected machines from the network to prevent them from participating in botnet activities (like DDoS) or spreading laterally via SMB.",
    "Block known IRC ports (6667-6669) at the perimeter firewall to sever the C2 connection for all infected bots.",
    "Mandate a physical sweep and format of all unapproved USB flash drives used within the organization."
  ],
  "what_to_avoid": [
    "Do not insert a suspected infected USB drive into an unprotected machine for analysis without disabling Autorun first.",
    "Avoid assuming a single cleaned machine means the incident is over; worms propagate rapidly, and other infected machines will simply re-infect it."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ],
  "attack_stage": [
    "execution",
    "persistence"
  ],
  "ecosystem": [
    "windows_pe"
  ],
  "is_emerging": false,
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows Server 2022",
    "Windows Server 2019"
  ]
}