Msilkrypt

Overview

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.

Understanding Msilkrypt
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.

Execution and Encryption Strategies
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.

Indicators of Compromise & Impact
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.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_MSILKRYPT {
    meta:
        description = "Detects Msilkrypt (ransomware)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "msilkrypt" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Msilkrypt Activity
id: d1289d1fab9e086d9376a3ed08ea0e8a
status: experimental
description: Detects generic indicators of the msilkrypt malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*msilkrypt*"
    condition: selection
level: medium

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. 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.
2. Do not reboot the machine if it is currently encrypting; rebooting can destroy cryptographic material in RAM that might be needed for decryption.
3. 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).
4. Begin the incident response process to restore data from secure, offline backups.

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not pay the ransom. Paying funds criminal syndicates and there is zero guarantee the attackers will provide a working decryption tool.
2. Avoid connecting external hard drives or network shares to the infected machine, as the ransomware will encrypt those as well.

References & External Analysis

• Search "msilkrypt" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: ransomware)

Explore other malware families in the same category:

• Headache
• Loyeetro
• Togapy
• Emogen
• Vake

Machine-readable

Get this profile as JSON: https://jordan123234-malware-families-explorer.static.hf.space/api/msilkrypt.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.