{
  "family": "mbrlock",
  "sample_count": 7,
  "category": "ransomware",
  "description": "Ransom:Win32/Mbrlock represents a highly destructive class of ransomware known as **Bootlockers**. Unlike traditional file-encrypting ransomware that targets individual documents (like Word or PDF files), Mbrlock targets the foundational architecture of the hard drive itself. It specifically overwrites the Master Boot Record (MBR) of the infected system, preventing the Windows operating system from loading entirely and holding the entire computer hostage.<br><br><b>Understanding Bootlocker Ransomware</b><br>To an infected user, the impact is immediate and terrifying. Instead of the familiar Windows logo upon turning on the computer, they are greeted by a stark, text-only (DOS-like) screen demanding a ransom payment to unlock the system. For a security analyst, Mbrlock indicates a severe breach that requires low-level disk recovery techniques to remediate, as the operating system's boot process has been hijacked (`T1542.003`). Notable examples of Mbrlock-style malware include the early versions of Petya and various 'lock-screen' extortion variants.<br><br><b>Execution and Boot Hijacking Mechanics</b><br>Mbrlock is often distributed via spear-phishing or dropped as a secondary payload by other trojans. Upon execution (`T1204.002`), it requires administrative privileges. Once obtained, it uses low-level disk writing APIs (like `DeviceIoControl`) to access `PhysicalDrive0` directly. It backs up the legitimate Master Boot Record (MBR), encrypts or obfuscates it, and then overwrites the active MBR with its own malicious, custom bootloader (`T1542.003`). Finally, it forces a system reboot (`T1529`). When the BIOS/UEFI attempts to boot the computer, it loads the malicious Mbrlock code instead of the Windows bootloader, displaying the ransom note and preventing OS initialization.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is total denial of service for the endpoint. The primary IoC is the inability to boot into Windows, replaced by a text-mode ransom note. EDR systems monitoring for low-level disk access (`T1006`) will often flag the attempt to overwrite the MBR if they are active before the reboot. Because the OS never loads, traditional antivirus cannot run to remove the threat once the system has rebooted.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1006",
    "T1486",
    "T1542.003",
    "T1529"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1542.003",
      "name": "Pre-OS Boot: Bootkit (Overwriting the Master Boot Record)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1529",
      "name": "System Shutdown/Reboot (Forcing reboot to trigger the bootlocker)",
      "tactic": "Impact"
    },
    {
      "id": "T1486",
      "name": "Data Encrypted for Impact (Encrypting the original MBR or MFT)",
      "tactic": "Impact"
    },
    {
      "id": "T1006",
      "name": "Direct Volume Access (Required to overwrite Sector 0)",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Do not pay the ransom. Mbrlock variants are often poorly coded, and paying does not guarantee a working unlock code.",
    "Boot the infected system using a legitimate Windows Recovery Environment (WinRE) USB drive or a Linux Live CD.",
    "Use the `bootrec.exe /fixmbr` command (or equivalent Linux utilities like `testdisk`) to overwrite the malicious bootloader with a standard Windows MBR, restoring the ability to boot.",
    "Once booted back into Windows, immediately perform a full offline antivirus scan to remove the initial dropper executable that caused the infection."
  ],
  "what_to_avoid": [
    "Do not format the hard drive immediately; the actual user files are often untouched (unless it's a destructive wiper variant like NotPetya), and restoring the MBR usually recovers the entire system intact.",
    "Avoid turning the computer on and off repeatedly; if the malware also encrypted the Master File Table (MFT), this could cause further corruption."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}