{
  "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": [],
  "faq_count": 0,
  "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": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}