{
  "family": "zero",
  "sample_count": 1,
  "category": "ransomware",
  "description": "<h3>Executive Summary</h3>\nWhile \"Zero\" can occasionally refer to minor ransomware variants, in enterprise security contexts, it most commonly refers to the ZeroAccess botnet (also known as Sirefef). ZeroAccess is a highly sophisticated, kernel-level rootkit designed to completely subjugate Windows systems. Its primary objective is to create a massive peer-to-peer (P2P) botnet utilized for highly profitable click fraud campaigns and Bitcoin mining, operating entirely invisibly to the user.\n\n<h3>Infection Vector and Technical Capabilities</h3>\nZeroAccess is typically distributed via exploit kits (like Blackhole) hosted on compromised websites, which silently exploit unpatched browser or Java vulnerabilities. It is also distributed via malicious software bundlers on peer-to-peer networks.\n\nUpon execution, ZeroAccess employs advanced, highly destructive rootkit techniques:\n<ul>\n<li><strong>Kernel-Level Hooking:</strong> The malware injects itself deep into the Windows operating system core (Ring 0). It actively overwrites critical system drivers (like `tcpip.sys`) to intercept and manipulate network traffic.</li>\n<li><strong>Security Software Neutralization:</strong> ZeroAccess aggressively hunts for and terminates processes associated with antivirus and EDR solutions. It also actively blocks updates to Windows Defender and other security tools.</li>\n<li><strong>Hidden Volumes:</strong> It creates hidden, encrypted volumes within the Windows file system (often masquerading as Recycle Bin data) to store its configuration files, downloaded payloads, and the stolen click-fraud data, making it invisible to standard file explorers and basic AV scans.</li>\n<li><strong>P2P Communication:</strong> Rather than relying on a centralized C2 server that can be easily taken down, infected nodes communicate directly with each other via a custom P2P protocol to receive updates and new instructions.</li>\n</ul>\n\n<h3>Threat Assessment</h3>\nA ZeroAccess infection is a critical compromise of system integrity. The malware's ability to operate at the kernel level means it completely controls the operating system's reality. It causes severe network congestion (due to P2P chatter and click fraud traffic) and leaves the machine completely defenseless against other malware.\n\n<h3>Incident Response and Remediation</h3>\n<ul>\n<li><strong>Immediate Network Severance:</strong> Isolate the endpoint to halt the click fraud traffic and prevent it from acting as a node in the P2P botnet.</li>\n<li><strong>Do Not Attempt Cleaning:</strong> Because ZeroAccess overwrites critical system drivers and utilizes encrypted rootkit volumes, attempting to manually clean the infection or run standard AV removal tools will almost certainly result in a permanently unbootable system (Blue Screen of Death).</li>\n<li><strong>Total Re-imaging:</strong> The only secure and reliable remediation for a ZeroAccess/Sirefef infection is a complete bare-metal wipe of the hard drive and a fresh OS installation from a known-good baseline.</li>\n</ul>",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [
    "Rootkit.ZeroAccess",
    "Trojan.Sirefef",
    "Win32/ZeroAccess"
  ],
  "enrichment_level": "expert-seo",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Zero and what threat category does it belong to?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Zero 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 Zero establish persistence and evade defensive controls?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Zero 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 Zero compromise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Security teams responding to Zero 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 Rootkit.ZeroAccess employ during execution?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Rootkit.ZeroAccess 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 Rootkit.ZeroAccess, and what is the recommended recovery procedure?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Decryption availability for Rootkit.ZeroAccess 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": [
    "T1014",
    "T1562.001",
    "T1090.003",
    "T1564"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-10-15",
  "type": "Rootkit / Botnet",
  "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": "T1014",
      "name": "Rootkit (Hiding files and processes)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1562.001",
      "name": "Impair Defenses: Disable or Modify Tools",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1090.003",
      "name": "Proxy: Multi-hop Proxy (Use of Tor/I2P for C2)",
      "tactic": "Command and Control"
    },
    {
      "id": "T1564",
      "name": "Hide Artifacts",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Immediately isolate affected host(s) from the internal network (disconnect physical Ethernet and disable Wi-Fi/Bluetooth) to prevent Zero 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 Zero 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 Zero 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 Zero 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 Zero.",
    "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 Zero eradication is completely verified."
  ],
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows Server 2022",
    "Windows Server 2019"
  ]
}