Msilkrypt
Table of Contents
Overview
MsilKrypt (cataloged across security intelligence feeds under signatures including VirTool:MSIL/MsilKrypt, Trojan:MSIL/Krypt, and VirTool:MSIL/Kryptik) is an obfuscated .NET crypter, runtime unpacker, and binary protector framework active since 2014. Widely traded on underground cybercrime forums, MsilKrypt is engineered to wrap raw binary payloads—including commodity infostealers (Agent Tesla, Formbook), remote access trojans (AsyncRAT), and ransomware stagers—inside legitimate-looking .NET assemblies. Upon execution, MsilKrypt resolves AES or XOR decryption keys dynamically from embedded managed resources, bypasses the Windows Antimalware Scan Interface (AMSI) and Event Tracing for Windows (ETW) via memory patching, and injects the decrypted payload directly into memory using reflective Assembly.Load or process hollowing into trusted Windows binaries such as RegAsm.exe or AppLaunch.exe.
Known aliases
Threat reports may refer to this family under multiple names:
Family Pedigree & Lineage
Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:
Known Derivatives & Downstream Variants: Virtool:Msil/Msilkrypt.A · Virtool:Msil/Msilkrypt.B
MITRE ATT&CK Techniques
This family has been observed using the following ATT&CK techniques: T1027.002 · T1055.012 · T1562.001 · T1140 · T1547.001
MITRE D3FEND™ Defensive Countermeasures
Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-EDA | Executable Deobfuscation Analysis | Detect | T1027.002 | Deploy static entropy scanners and dynamic memory-unpacking heuristics to identify obfuscated and packed PE structures. |
D3-PHA | Process Hollowing Analysis | Detect | T1055.012 | Inspect unbacked executable memory regions (PAGE_EXECUTE_READWRITE) for replaced PE image headers inside legitimate host processes. |
D3-RPM | Registry Persistence Monitoring | Detect | T1547.001 | Audit and restrict write privileges to user and machine-level Registry Run/RunOnce keys using Endpoint Privilege Management. |
D3-STA | Security Tool Anti-Tamper Enforcement | Harden | T1562.001 | Block unauthorized modification of antivirus registry flags and prevent stopping security agent services. |
Tiered Detection Rules (Cisco CAIRN Model)
Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:
Tier 1 Primitive Artifact Rule (Fast Triage)
Matches raw strings and file markers. Vulnerable to binary repacking and simple obfuscation.
rule MALWARE_WIN_MSILKRYPT_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Msilkrypt"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "msilkrypt" ascii wide nocase
$s2 = "virtool:msil/msilkrypt" ascii wide nocase
$s3 = "trojan:msil/krypt" ascii wide nocase
$s4 = "virtool:msil/kryptik" ascii wide nocase
$s5 = "msil/msilkrypt" ascii wide nocase
$s6 = "trojan:msil/msilkrypt.a" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Tier 2 Behavioral Context Rule (Process Chains & Sigma)
Tracks parent-child process anomalies and suspicious scripting telemetry. Resilient against file renames.
title: SystemHelpDesk Detection - Msilkrypt (Crypter) Execution & Triage
id: 60781a80-97fb-5b27-9430-1e049e196320
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Msilkrypt malware family. Detects suspicious execution from temporary user
directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/msilkrypt
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.crypter
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1027_002
- attack.t1055_012
- attack.t1562_001
- attack.t1140
- attack.t1547_001
logsource:
category: process_creation
product: windows
detection:
selection_process:
Image|endswith:
- \cmd.exe
- \powershell.exe
- \cscript.exe
- \wscript.exe
CommandLine|contains:
- AppData\Local\Temp
- -WindowStyle Hidden
- /e:jscript
- bitsadmin /transfer
condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: mediumTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_MSILKRYPT_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Msilkrypt tradecraft"
tier = "T3 - Attribution Fingerprint"
confidence = "High (Confirmed Family Signature)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
// Core family identifier & heuristic payload signatures
$attrib_str = "msilkrypt" ascii wide nocase
$pe_magic = "MZ" ascii
$net_marker = "http" ascii nocase
condition:
uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}References & External Analysis
- Microsoft Defender Threat Encyclopedia - VirTool:MSIL/MsilKrypt
- Trend Micro Threat Encyclopedia - VirTool.MSIL.Kryptik
- Search "msilkrypt" on VirusTotal (External Analysis)
- Search "msilkrypt" on Any.Run (Sandbox Sandbox)
- Search "msilkrypt" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is VirTool:MSIL/MsilKrypt?
MsilKrypt is an obfuscated .NET crypter and loader used by cybercriminals to package and hide commodity trojans from antivirus scanners.
How does MsilKrypt bypass antivirus detections?
It bypasses AMSI and ETW via in-memory byte patching and decrypts nested payloads dynamically inside memory without touching disk.
What payloads are commonly protected with MsilKrypt?
Threat actors use MsilKrypt to protect infostealers (Agent Tesla, Formbook), RATs (AsyncRAT, Remcos), and ransomware loaders.
How does MsilKrypt execute the decrypted payload?
It uses reflective assembly loading or process hollowing into trusted .NET executables like RegAsm.exe or AppLaunch.exe.
How can defenders detect MsilKrypt crypter binaries?
Deploy AMSI memory monitoring, inspect high-entropy embedded resources in .NET binaries, and detect abnormal child process creation from RegAsm.exe.
How do I remove the Msilkrypt Crypter from Windows?
Manual removal of Msilkrypt is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.
Is Msilkrypt a virus or a Crypter?
Msilkrypt is classified as a Crypter. Unlike traditional viruses that infect files, modern malware like Msilkrypt typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Msilkrypt infection?
Symptoms of Msilkrypt can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.
Protect Your Network Against Crypters
Want to prevent Msilkrypt and similar threats from compromising your organization? Read our comprehensive defensive guide: Think You've Been Hacked? What To Do First.
📣 Threat Intel Correction or Update?
Notice an outdated IOC, unlisted alias, or disputed attribution? Threat researchers are invited to propose an update on GitHub or contact the SystemHelpDesk research desk. All community revisions are credited in our public CHANGELOG.
Machine-readable
Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/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.