{
  "family": "obfusransom",
  "sample_count": 1,
  "category": "ransomware",
  "description": "Ransomware:Win32/Obfusransom is a highly critical, heuristic detection string utilized by antivirus engines (specifically Microsoft Defender) to flag a file that is actively exhibiting ransomware behaviors (`T1486`), but whose static signature has been heavily obfuscated, packed, or encrypted (`T1027`) to bypass traditional detection. This detection indicates that a ransomware payload is likely executing *right now* on the endpoint.<br><br><b>Understanding Obfusransom (Heuristic Ransomware Detection)</b><br>To an end-user, this detection often happens too late—as files are actively being encrypted, or right before the ransom note is dropped. For an incident response team, an 'Obfusransom' alert is a 'Break Glass' emergency. It means a threat actor has already bypassed perimeter defenses, delivered a payload, and initiated the final, destructive phase of the attack.<br><br><b>Execution and Obfuscation Mechanics</b><br>The file triggering the 'Obfusransom' alert is typically a custom-packed variant of a known ransomware family (like LockBit, Conti, or BlackCat). The attacker uses commercial or custom packers (`T1027.002`) so the file hash doesn't match any known threats. However, when the file executes, the AV engine detects its *behavior*: the rapid opening, encrypting, and renaming of hundreds of user files in quick succession (`T1486`), the deletion of Volume Shadow Copies via `vssadmin.exe` (`T1490`), or the dropping of `.txt` or `.html` ransom notes.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is immediate, catastrophic data loss and extortion. Host-based IoCs include EDR alerts for mass file modification, the execution of `vssadmin.exe delete shadows /all /quiet` or `wbadmin delete catalog -quiet`, and the presence of encrypted files with anomalous extensions (e.g., `.locked`, `.crypted`). Network IoCs may include large data exfiltration (double extortion) immediately preceding the encryption event.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [
    {
      "@type": "Question",
      "name": "What is Obfusransom and what threat category does it belong to?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Obfusransom 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 Obfusransom establish persistence and evade defensive controls?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Obfusransom 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 Obfusransom compromise?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Security teams responding to Obfusransom 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 Obfusransom employ during execution?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Obfusransom 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 Obfusransom, and what is the recommended recovery procedure?",
      "acceptedAnswer": {
        "@type": "Answer",
        "text": "Decryption availability for Obfusransom 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": [
    "T1486",
    "T1027",
    "T1490"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1486",
      "name": "Data Encrypted for Impact (The core behavior triggering the heuristic alert)",
      "tactic": "Impact"
    },
    {
      "id": "T1027",
      "name": "Obfuscated Files or Information (The reason it was flagged heuristically rather than by a specific family name)",
      "tactic": "Defense Evasion"
    },
    {
      "id": "T1490",
      "name": "Inhibit System Recovery (Deleting shadow copies to prevent restoration)",
      "tactic": "Impact"
    }
  ],
  "containment_steps": [
    "IMMEDIATELY isolate the affected endpoint from the network by physically unplugging the Ethernet cable or disabling the NIC; do not gracefully shut it down.",
    "Do NOT reboot the machine, as this will destroy the encryption keys that might currently reside in volatile memory (RAM).",
    "Capture a full memory dump (RAM) immediately; researchers may be able to extract the symmetric encryption keys from memory to decrypt files.",
    "Initiate a full, enterprise-wide incident response protocol to identify lateral movement and determine if data was exfiltrated."
  ],
  "what_to_avoid": [
    "Do NOT reboot the affected machine or turn it off normally; pull the plug or isolate the NIC.",
    "Do NOT pay the ransom without consulting professional incident response and law enforcement agencies."
  ],
  "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,
  "target_platforms": [
    "Windows 11",
    "Windows 10",
    "Windows Server 2022",
    "Windows Server 2019"
  ]
}