Msilpack
Overview
Executive Summary
MSILPack (or MSIL/Packer) is a heuristic detection identifying a malicious file that has been wrapped, obfuscated, or compiled using a .NET (MSIL - Microsoft Intermediate Language) packer or protector (such as ConfuserEx, .NET Reactor, or custom cryptors). Threat actors heavily utilize MSIL packers to cloak highly destructive payloads—specifically commodity Info-Stealers like AgentTesla, RedLine, and Snake Keylogger—from static antivirus detection.Technical Capabilities and Evasion
An MSILPack detection does not indicate a specific malware family; rather, it indicates the method used to hide the true malware. .NET applications are easily decompiled, so attackers use these packers to encrypt the core malicious logic. When an MSILPack executable is run, it performs a complex "unpacking" routine entirely in memory:- Memory Decryption: The outer .NET wrapper executes and decrypts the primary payload (the actual malware) directly into the system's RAM. The decrypted payload never touches the physical hard drive, completely bypassing traditional, disk-based antivirus scanning.
- Process Hollowing / RunPE: The unpacked payload often utilizes a technique called "RunPE." The wrapper spawns a legitimate Windows process (like `RegAsm.exe` or `vbc.exe`) in a suspended state, hollows out its legitimate memory, injects the decrypted malicious .NET assembly, and resumes the process.
- Payload Execution: The true malware (e.g., AgentTesla) now runs under the guise of a trusted Microsoft process, communicating with its C2 server and exfiltrating stolen browser credentials, keystrokes, and session tokens.
Threat Assessment
The execution of an MSILPack-obfuscated file is a critical incident. The presence of this packing technique almost universally guarantees the deployment of an advanced Info-Stealer or RAT. Because the payload runs in memory, traditional AV will often report the system as "clean" while the malware actively exfiltrates data.Incident Response and Remediation
- Behavioral Analysis (EDR): Static AV is blind to this threat. Remediation requires an EDR solution capable of monitoring memory allocation and terminating processes exhibiting "RunPE" or Process Hollowing behaviors.
- Network Isolation and Triage: Isolate the machine immediately. Analyze network traffic to identify the C2 server the injected process is communicating with.
- Assume Credential Compromise: Due to the massive prevalence of .NET-packed Info-Stealers, all local and domain credentials stored or used on the compromised endpoint must be immediately reset.
Known aliases
Threat reports may refer to this family under multiple names:
MITRE ATT&CK Techniques
This family has been observed using the following ATT&CK techniques: T1027.002 T1055.002 T1055.012
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_MSILPACK {
meta:
description = "Detects Msilpack (advanced_threat)"
author = "SystemHelpdesk Boilerplate Generator"
date = "2026-07-06"
strings:
$s1 = "msilpack" ascii wide nocase
$s2 = "trojan.msil.packer" ascii wide nocase
$s3 = "msil/cryptor" ascii wide nocase
$s4 = "win32/msilpack" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Sigma Rule
title: Suspicious Msilpack Activity
id: bd002626be156753852718c28ebdb0e4
status: experimental
description: Detects generic indicators of the msilpack malware family.
logsource:
category: process_creation
product: windows
detection:
selection:
Image|endswith:
- '\cmd.exe'
- '\powershell.exe'
CommandLine|contains:
- "*msilpack*"
- "*trojan.msil.packer*"
- "*msil/cryptor*"
- "*win32/msilpack*"
condition: selection
level: mediumReferences & External Analysis
- Search "msilpack" on VirusTotal (External Analysis)
Frequently Asked Questions
How do I remove the Msilpack Advanced_Threat from Windows?
Manual removal of Msilpack 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 Msilpack a virus or a Advanced_Threat?
Msilpack is classified as a Advanced_Threat. Unlike traditional viruses that infect files, modern malware like Msilpack typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Msilpack infection?
Symptoms of Msilpack 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.
Related Families (Category: advanced_threat)
Explore other malware families in the same category:
Protect Your Network Against Advanced_Threats
Want to prevent Msilpack and similar threats from compromising your organization? Read our comprehensive defensive guide: Suspect an Infection? What to do.
Machine-readable
Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/msilpack.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.