{
  "family": "kelvir",
  "sample_count": 1,
  "category": "trojan",
  "description": "<h3>Executive Summary</h3>\nKelvir is a widespread and aggressive family of Worms that primarily propagate by exploiting instant messaging networks, most notably the legacy MSN Messenger (Windows Live Messenger) platform. Emerging in the mid-2000s, Kelvir rapidly infected millions of computers globally. By hijacking the victim's IM client and leveraging social engineering, Kelvir rapidly spreads across contact lists, degrading network performance and often dropping secondary backdoor trojans.\n\n<h3>Propagation and Execution Lifecycle</h3>\nKelvir relies on aggressive, largely automated propagation techniques utilizing social engineering:\n<ul>\n<li><strong>Instant Messaging Propagation (Worm Capability):</strong> Upon execution, Kelvir hooks into the active MSN Messenger process. It automatically sends a malicious link to every contact in the infected user's active contact list. The message often uses enticing social engineering (e.g., \"lol check out this picture of you!\") to trick the recipient into clicking the link.</li>\n<li><strong>Payload Delivery:</strong> The link directs the recipient to a compromised web server that automatically downloads the Kelvir executable (often disguised as a `.scr`, `.pif`, or `.zip` file). If the new victim executes the file, the cycle repeats.</li>\n<li><strong>System Sabotage and Backdoors:</strong> Once active, Kelvir attempts to disable local antivirus and firewall software. Crucially, many Kelvir variants carry a secondary payload—often a botnet agent or a backdoor trojan (like Spybot)—allowing the attacker to remotely control the infected machine, steal credentials, or launch DDoS attacks.</li>\n</ul>\n\n<h3>Threat Assessment</h3>\nWhile the specific MSN Messenger platform is obsolete, the propagation mechanics of Kelvir (abusing trusted communication channels) remain highly relevant today (e.g., spreading via Slack, Teams, or WhatsApp). An infection represents a significant security incident, as the rapid propagation can overwhelm network bandwidth and the secondary payloads compromise endpoint integrity.\n\n<h3>Eradication and Incident Response</h3>\n<ul>\n<li><strong>Aggressive Network Isolation:</strong> Infected machines must be immediately disconnected from the LAN to halt the outbound IM spam traffic and prevent further lateral spread.</li>\n<li><strong>Application Control and Web Filtering:</strong> In modern environments, implement strict web filtering (SWG) to block the download of executable file types from unknown domains, neutralizing the worm's primary delivery mechanism.</li>\n<li><strong>Behavioral EDR:</strong> Defenses must rely on heuristic EDR tools that detect anomalous actions (e.g., an IM client process unexpectedly attempting to download and execute secondary binaries, or modifications to the Windows `HOSTS` file).</li>\n</ul>",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [
    "Worm.Win32.Kelvir",
    "IM-Worm.Kelvir",
    "W32/Kelvir"
  ],
  "enrichment_level": "expert-seo",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Kelvir and what threat category does it belong to?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Kelvir is classified as a Trojan. 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 Kelvir establish persistence and evade defensive controls?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Kelvir 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 Kelvir compromise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Security teams responding to Kelvir 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 secondary payloads and staging behaviors are commonly associated with Worm.Win32.Kelvir?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Worm.Win32.Kelvir frequently operates as a loader or dropper designed to establish a foothold before downloading and executing secondary high-impact malware payloads. Depending on the threat actor's objectives, these dropped modules can range from ransomware and banking injects to modular infostealers and remote management backdoors."
      }
    },
    {
      "@type": "Question",
      "name": "How can security operations teams effectively detect and hunt for Worm.Win32.Kelvir across enterprise endpoints?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Defenders should hunt for Worm.Win32.Kelvir by deploying behavioral endpoint detection and response (EDR) rules that monitor suspicious process spawning (such as cmd.exe or powershell.exe spawned from office documents or temporary directories), anomalous outbound network connections from non-browser binaries, and unauthorized modifications to Windows Run keys and scheduled task registries."
      }
    }
  ],
  "faq_count": 5,
  "mitre_attack": [
    "T1566.002",
    "T1562.001",
    "T1059"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-10-15",
  "type": "Worm",
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ],
  "attack_stage": [
    "execution",
    "persistence"
  ],
  "ecosystem": [
    "windows_pe"
  ],
  "is_emerging": false,
  "mitre_attack_detail": [
    {
      "id": "T1566.002",
      "name": "Phishing: Spearphishing Link (Social engineering to force the user to download the tool)",
      "tactic": "Initial Access"
    },
    {
      "id": "T1562.001",
      "name": "Impair Defenses: Disable or Modify Tools",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1059",
      "name": "Command and Scripting Interpreter",
      "tactic": "Execution"
    }
  ],
  "containment_steps": [
    "Sever network connectivity for the flagged endpoint to terminate persistent command-and-control (C2) communication channels and stop Kelvir from retrieving secondary stage payloads.",
    "Capture process memory triage to detect and terminate malicious threads injected by Kelvir into legitimate system processes such as explorer.exe or svchost.exe.",
    "Audit Windows Registry Run keys (HKCU\\Software\\Microsoft\\Windows\\CurrentVersion\\Run) and Task Scheduler entries to locate and purge Kelvir persistence hooks.",
    "Deploy updated enterprise EDR detection signatures and conduct an out-of-band endpoint scan to isolate dropped binaries and staged payloads.",
    "Rotate all credentials, domain user passwords, and session cookies active on the system during the Kelvir execution timeframe."
  ],
  "what_to_avoid": [
    "Do not assume the incident is resolved simply because an antivirus tool removed the initial Kelvir dropper; always verify that secondary payloads and persistence hooks have been eradicated.",
    "Avoid logging in with Domain Admin or privileged credentials on a machine suspected of running Kelvir until memory triage is complete.",
    "Do not delay host isolation; automated lateral movement and credential dumping can occur within minutes of initial execution."
  ],
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows 7"
  ]
}