{
  "family": "lurk",
  "sample_count": 1,
  "category": "ransomware",
  "description": "<h3>Executive Summary</h3>\nLurk refers to both a highly sophisticated Trojan Downloader and the infamous Russian cybercriminal syndicate that created it. The Lurk group was primarily known for orchestrating massive financial heists against Russian and Eastern European banks, stealing millions of dollars before their arrest. The Lurk trojan itself is a modular, fileless malware designed specifically for stealthy infiltration, reconnaissance, and the deployment of specialized banking modules or ransomware.\n\n<h3>Infection Vector and Technical Capabilities</h3>\nThe Lurk group heavily utilized strategic web compromises (watering hole attacks) and the \"Angler\" Exploit Kit to distribute the malware. By compromising legitimate news sites or forums frequented by their targets, they could silently infect systems via drive-by downloads without requiring user interaction.\n\nLurk is renowned for its advanced, \"fileless\" architecture:\n<ul>\n<li><strong>In-Memory Execution:</strong> Lurk was one of the first major malware families to operate almost entirely in RAM. The initial exploit executes a small loader that downloads the main payload as an encrypted DLL. This DLL is injected directly into a legitimate process (like `explorer.exe` or `iexplore.exe`) and never touches the physical hard drive, rendering traditional, signature-based AV completely blind.</li>\n<li><strong>Modular Architecture:</strong> The core Lurk trojan is a sophisticated backdoor that acts as a staging platform. The C2 server can push highly customized modules to the infected machine based on the target's value, including specialized banking credential stealers, network reconnaissance tools, or keyloggers.</li>\n<li><strong>Network Evasion:</strong> Lurk utilizes custom encryption protocols and frequently rotates its command-and-control (C2) domains (often using DGAs or compromised legitimate domains) to evade network-level detection and perimeter blocking.</li>\n</ul>\n\n<h3>Threat Assessment</h3>\nA Lurk infection is a critical, \"Code Red\" security incident. It indicates a highly targeted attack by an Advanced Persistent Threat (APT)-level criminal syndicate. The malware's primary goal is massive financial theft or, in later campaigns, the deployment of destructive ransomware across the enterprise network.\n\n<h3>Incident Response and Remediation</h3>\n<ul>\n<li><strong>Memory Forensics:</strong> Because Lurk is a fileless threat, traditional disk forensics will yield little evidence. Responders must utilize advanced memory analysis tools (like Volatility) to capture RAM dumps, identify the injected malicious threads, and extract the decrypted payload.</li>\n<li><strong>Network Isolation and Triage:</strong> Isolate the infected machine immediately to sever C2 communication and prevent lateral movement. Analyze corporate firewall and proxy logs to identify the compromised \"watering hole\" website that initiated the infection.</li>\n<li><strong>Complete Re-imaging:</strong> Due to the sophisticated in-memory capabilities and the likelihood of lateral movement, the only secure remediation is a complete bare-metal wipe and re-image of the compromised endpoint from a clean baseline.</li>\n</ul>",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [
    "Trojan.Lurk",
    "Banker.Lurk",
    "Win32/Lurk"
  ],
  "enrichment_level": "expert-seo",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Lurk and what threat category does it belong to?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Lurk is classified as a Ransomware. 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 Lurk establish persistence and evade defensive controls?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Lurk 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 Lurk compromise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Security teams responding to Lurk 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 cryptographic algorithms and file targeting techniques does Trojan.Lurk employ during execution?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Trojan.Lurk typically leverages hybrid cryptographic architectures combining symmetric stream or block ciphers (such as AES-256 or ChaCha20) for rapid file encryption with asymmetric algorithms (such as RSA-2048 or Curve25519) to securely protect the session keys. It aggressively targets sensitive file extensions including corporate documents, databases, virtual disks, and backups while systematically executing commands to delete Volume Shadow Copies (vssadmin delete shadows /all /quiet) and disable system recovery options."
      }
    },
    {
      "@type": "Question",
      "name": "Are decryptors available for Trojan.Lurk, and what is the recommended recovery procedure?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Decryption availability for Trojan.Lurk depends on whether security researchers or law enforcement (such as the No More Ransom initiative) have recovered the master private keys or discovered flaws in its key generation routines. Victims should never pay the extortion demand, as payment fuels criminal operations without guaranteeing file restoration. The recommended recovery procedure entails isolating infected hosts, conducting forensic disk imaging, identifying the root access vector, and restoring validated systems from immutable offline backups."
      }
    }
  ],
  "faq_count": 5,
  "mitre_attack": [
    "T1055.001",
    "T1105",
    "T1189",
    "T1568.002"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-10-15",
  "type": "Trojan / Downloader",
  "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,
  "mitre_attack_detail": [
    {
      "id": "T1055.001",
      "name": "Dynamic-link Library Injection",
      "tactic": "defense-evasion"
    },
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer",
      "tactic": "Command and Control"
    },
    {
      "id": "T1189",
      "name": "Drive-by Compromise",
      "tactic": "Initial Access"
    },
    {
      "id": "T1568.002",
      "name": "Dynamic Resolution: Domain Generation Algorithms (DGA) (Evading C2 blacklisting)",
      "tactic": "Command and Control"
    }
  ],
  "containment_steps": [
    "Immediately isolate affected host(s) from the internal network (disconnect physical Ethernet and disable Wi-Fi/Bluetooth) to prevent Lurk from spreading laterally or encrypting network-attached storage (NAS) and shared SMB volumes.",
    "Preserve volatile system memory (RAM capture) on a representative endpoint before attempting a reboot or power-down, as Lurk symmetric encryption keys or uncompiled payload components may still reside in memory.",
    "Audit process execution logs and terminate active scripting interpreters (e.g. PowerShell, CMD, WScript) or commands executing 'vssadmin.exe delete shadows' or 'wbadmin' used by Lurk to inhibit recovery.",
    "Investigate the initial compromise vector (such as exposed RDP instances, spearphishing attachments, or vulnerable edge gateways) and enforce an immediate credential reset for all compromised Active Directory accounts.",
    "Restore critical assets and databases exclusively from verified, air-gapped, or immutable offline backups once the Lurk binary and related persistence hooks are eradicated."
  ],
  "what_to_avoid": [
    "Do not restart or power cycle infected systems prematurely; doing so destroys volatile RAM encryption keys and may trigger bootloader locking logic embedded in Lurk.",
    "Avoid negotiating or paying the extortion demand without prior forensic evaluation and consultation with incident response specialists, as payment does not guarantee data recovery.",
    "Do not connect clean backup drives or external storage to the affected network until Lurk eradication is completely verified."
  ],
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows Server 2022",
    "Windows Server 2019"
  ]
}