{
  "family": "msilkrypt",
  "sample_count": 28,
  "category": "ransomware",
  "description": "Ransomware:Win32/Msilkrypt is a heuristic detection for ransomware variants that are developed using the Microsoft .NET Framework (MSIL - Microsoft Intermediate Language). These variants are designed to rapidly encrypt user files and demand a cryptocurrency payment in exchange for the decryption key.<br><br><b>Understanding Msilkrypt</b><br>To the victim, an Msilkrypt infection is a catastrophic event. Their documents, photos, and databases are suddenly inaccessible, replaced by files with unusual extensions, accompanied by a demanding ransom note. For a security analyst, the 'MSIL' designation is significant. Because the ransomware is written in .NET, it is often easier to reverse-engineer using tools like dnSpy or ILSpy compared to malware written in C++ or Assembly. However, attackers counter this by utilizing heavily customized obfuscators (like ConfuserEx) to protect their .NET code.<br><br><b>Execution and Encryption Strategies</b><br>Msilkrypt variants are typically distributed via malicious email attachments (phishing), Remote Desktop Protocol (RDP) brute-forcing, or exploit kits. Upon execution, the malware often uses Vssadmin to delete Volume Shadow Copies (`T1490`), preventing easy system restoration. It then traverses the file system, searching for specific file extensions (e.g., `.doc`, `.xls`, `.jpg`, `.sql`). It encrypts these files using strong cryptography (often a hybrid of AES for the files and RSA to protect the AES key). The malware then drops a ransom note (typically a `.txt` or `.hta` file) detailing the payment instructions.<br><br><b>Indicators of Compromise & Impact</b><br>The impact is immediate and severe data loss, potentially halting business operations. EDR platforms should alert on the mass modification of files and the execution of `vssadmin.exe delete shadows`. Network logs may show the malware communicating with a C2 server to exchange cryptographic keys prior to encryption. The presence of the ransom notes and encrypted files is the most obvious IoC.",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [],
  "enrichment_level": "expert-seo",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1486",
    "T1105",
    "T1027",
    "T1490",
    "T1059.003"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-06-09",
  "mitre_attack_detail": [
    {
      "id": "T1486",
      "name": "Data Encrypted for Impact",
      "tactic": "Impact"
    },
    {
      "id": "T1490",
      "name": "Inhibit System Recovery",
      "tactic": "Impact"
    },
    {
      "id": "T1059.003",
      "name": "Command and Scripting Interpreter: Windows Command Shell",
      "tactic": "Execution"
    },
    {
      "id": "T1105",
      "name": "Ingress Tool Transfer",
      "tactic": "Command and Control"
    },
    {
      "id": "T1027",
      "name": "Obfuscated Files or Information",
      "tactic": "Defense Evasion"
    }
  ],
  "containment_steps": [
    "Instantly isolate the endpoint from the network by pulling the physical cable or disabling the virtual NIC. Do NOT just turn off Wi-Fi, as the encryption is actively running.",
    "Do not reboot the machine if it is currently encrypting; rebooting can destroy cryptographic material in RAM that might be needed for decryption.",
    "Identify the specific variant of Msilkrypt (often by the extension appended to the encrypted files or the ransom note) and check for known decryptors (e.g., NoMoreRansom).",
    "Begin the incident response process to restore data from secure, offline backups."
  ],
  "what_to_avoid": [
    "Do not pay the ransom. Paying funds criminal syndicates and there is zero guarantee the attackers will provide a working decryption tool.",
    "Avoid connecting external hard drives or network shares to the infected machine, as the ransomware will encrypt those as well."
  ],
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}