{
  "family": "grenam",
  "sample_count": 7,
  "category": "advanced_threat",
  "description": "Worm:Win32/Grenam (also known as a generic network worm or **File Infector**) is a self-replicating malware family that aggressively spreads across network shares and removable media. While older, its mechanics are highly destructive. Beyond propagation, Grenam acts as a polymorphic File Infector (`.exe` and `.dll` files), physically altering legitimate binaries to embed its malicious code, ensuring maximum persistence and complicating remediation.<br><br><b>Understanding the Grenam Worm</b><br>To an infected user, the computer might become highly unstable, and antivirus engines will suddenly start quarantining hundreds of previously safe programs. For security analysts, Grenam represents a severe incident. Because it alters legitimate system files, manually deleting the 'infected' files will destroy the operating system or the user's installed applications. The network worm aspect means the infection will rapidly spread to any unprotected node on the LAN.<br><br><b>Propagation and File Infection Mechanics</b><br>The infection cycle often begins via an infected USB drive (`T1091`) or an open network share (`T1080`). Upon execution (`T1204.002`), Grenam establishes persistence via multiple Registry Run keys. It begins scanning the local network for vulnerable SMB shares to copy itself into. Concurrently, it acts as a File Infector (`T1055.001`), searching the hard drive for executable files (`.exe`, `.scr`). It opens the target file, modifies the PE header, and appends its malicious, often polymorphically packed code. It then alters the entry point of the executable to point to the viral code. When the user later runs the 'infected' legitimate application, the worm code executes first, infects more files, and then passes control back to the legitimate application.<br><br><b>Indicators of Compromise & Impact</b><br>The primary impact is the widespread corruption of executable files, severe system instability, and network congestion. The most glaring IoC is an avalanche of EDR alerts indicating that hundreds of distinct, legitimate executables across the `C:\\` drive have changed their file hashes and sizes. Network logs will show a massive spike in SMB (Port 445) traffic as the worm attempts lateral movement.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Grenam and what threat category does it belong to?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Grenam 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 Grenam establish persistence and evade defensive controls?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Grenam 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 Grenam compromise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Security teams responding to Grenam 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 Grenam leverage in enterprise intrusions?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Grenam 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 Grenam maintain covert communications and evade perimeter network monitoring?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Grenam 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": [
    "T1055.001",
    "T1091",
    "T1083",
    "T1080"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1055.001",
      "name": "Process Injection: Dynamic-link Library Injection (File Infection logic)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1091",
      "name": "Replication Through Removable Media (USB worm propagation)",
      "tactic": "Lateral Movement"
    },
    {
      "id": "T1080",
      "name": "Taint Shared Content (Spreading via SMB shares)",
      "tactic": "Lateral Movement"
    },
    {
      "id": "T1083",
      "name": "File and Directory Discovery (Searching for executables to infect)",
      "tactic": "Discovery"
    }
  ],
  "containment_steps": [
    "Isolate the endpoint from the network instantly to halt the SMB propagation engine and stop it from infecting other workstations.",
    "Disable AutoRun and AutoPlay enterprise-wide via Group Policy for all removable media.",
    "Because Grenam is a file infector, you must use an enterprise antivirus solution capable of 'cleaning' (disinfecting) the appended malicious code from legitimate `.exe` files.",
    "If disinfection fails or the system is heavily corrupted, a complete OS rebuild from secure backups is required."
  ],
  "what_to_avoid": [
    "Do not blindly delete all files flagged by the AV; if they are infected system files, deleting them will render Windows unbootable.",
    "Avoid plugging a clean USB drive into the infected machine to transfer data, as the worm will immediately infect the drive."
  ],
  "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"
  ]
}