{
  "family": "krserv",
  "sample_count": 16,
  "category": "ransomware",
  "description": "KRServ (classified across antimalware research as Ransom:Win32/KRServ, Trojan:Win32/KRServ, and Win32/KRServ) is a specialized ransomware and trojan service family observed targeting corporate servers and enterprise infrastructure. Distributed via compromised remote access credentials, unpatched server vulnerabilities, or lateral movement tools, KRServ installs itself directly as a background Windows Service (`krserv.exe`) configured with Automatic startup under `HKLM\\System\\CurrentControlSet\\Services\\KRServ`. Executing under high-privilege `NT AUTHORITY\\SYSTEM` context, KRServ deploys asynchronous worker threads to traverse all local fixed disks, mounted network volumes, and removable media. It encrypts non-system files using robust AES-256 encryption, appending custom extensions and dropping ransom notes across traversed directories. Because it operates as an autonomous background service, KRServ persists across user logoffs and reboots, continuously monitoring the filesystem to encrypt newly created or modified files on the fly.",
  "cta": "Published by the SystemHelpdesk Threat Intelligence Team.",
  "aliases": [
    "Ransom:Win32/KRServ",
    "Trojan:Win32/KRServ",
    "Win32/KRServ",
    "KRServ Ransomware",
    "KRServ Service Trojan"
  ],
  "enrichment_level": "curated_sourced",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Ransom:Win32/KRServ?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "KRServ is a corporate ransomware family that operates as a persistent Windows Service under SYSTEM privileges to encrypt files."
      }
    },
    {
      "@type": "Question",
      "name": "Why does KRServ install itself as a Windows service?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Running as a service grants SYSTEM privileges, ensures persistence across logoffs, and allows continuous background file encryption."
      }
    },
    {
      "@type": "Question",
      "name": "What encryption methods does KRServ employ?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "It uses symmetric AES-256 file stream encryption combined with asymmetric master key encapsulation."
      }
    },
    {
      "@type": "Question",
      "name": "How does KRServ maintain continuous encryption on endpoints?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Its service threads continually poll the filesystem, locking new or modified documents as they are saved."
      }
    },
    {
      "@type": "Question",
      "name": "How should administrators neutralize KRServ infections?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Stop and delete the KRServ Windows service using sc.exe, isolate the host from the network, and restore data from offline backups."
      }
    }
  ],
  "faq_count": 5,
  "mitre_attack": [
    "T1486",
    "T1543.003",
    "T1490",
    "T1083",
    "T1135",
    "T1059.003"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-10-15",
  "mitre_attack_detail": [
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer",
      "tactic": "Command and Control"
    },
    {
      "id": "T1055",
      "name": "Process Injection",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1547.001",
      "name": "Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder",
      "tactic": "Persistence"
    },
    {
      "id": "T1566.001",
      "name": "Phishing: Spearphishing Attachment",
      "tactic": "Initial Access"
    },
    {
      "id": "T1027",
      "name": "Obfuscated Files or Information",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Isolate the endpoint immediately to prevent Krserv from downloading and executing its secondary payloads (e.g., ransomware).",
    "Audit the Windows Task Scheduler and Registry Run keys to identify and remove the Krserv persistence mechanisms.",
    "Review firewall and proxy logs to identify the C2 domains Krserv attempted to contact, and block them enterprise-wide.",
    "Capture a live memory image (RAM dump) to extract the injected Krserv modules and identify the secondary payloads."
  ],
  "what_to_avoid": [
    "Do not close an incident simply because the initial Krserv dropper was quarantined; always verify if secondary payloads were downloaded.",
    "Avoid relying solely on manual file deletion, as the injected processes will likely just recreate the dropped binaries."
  ],
  "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 - Ransom:Win32/KRServ",
      "url": "https://www.microsoft.com/en-us/wdsi/threats/malware-encyclopedia-description?Name=Ransom:Win32/KRServ"
    },
    {
      "name": "Kaspersky Threat Intelligence - Trojan-Ransom Overview",
      "url": "https://threats.kaspersky.com/en/threat/Trojan-Ransom.Win32/"
    },
    {
      "name": "MITRE ATT&CK - Create or Modify System Process: Windows Service (T1543.003)",
      "url": "https://attack.mitre.org/techniques/T1543/003/"
    }
  ],
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows Server 2022",
    "Windows Server 2019"
  ]
}