Msilbot

Overview

Executive Summary

Infection Vector and Technical Capabilities

• Just-In-Time (JIT) Compilation: The MSIL code is compiled into native machine code on the fly by the .NET runtime when executed, which can sometimes bypass simplistic behavioral analysis engines that struggle to monitor JIT processes.
• Comprehensive Botnet Functionality: Once active, the bot connects to a C2 server (often via HTTP or IRC) and awaits commands. Typical capabilities include downloading secondary payloads, executing arbitrary shell commands, launching DDoS attacks (UDP/TCP flooding), and acting as a proxy.
• Information Stealing: Many MSIL bots incorporate modules to scrape memory, log keystrokes, and extract saved credentials from web browsers and email clients.

Threat Assessment

Incident Response and Remediation

• Immediate Network Isolation: The highest priority is to disconnect the endpoint from the network to sever communication with the botnet C2 infrastructure and halt any active data exfiltration or DDoS participation.
• Behavioral Analysis (EDR): EDR solutions must be tuned to monitor the .NET runtime (`mscoree.dll`, `clr.dll`) for anomalous behavior, such as a supposedly benign application spawning `cmd.exe` or initiating high-volume outbound network connections.
• Complete Re-imaging: Due to the potential for the bot to have downloaded multiple secondary payloads and established deep persistence, attempting to manually "clean" the system is highly risky. A complete bare-metal wipe and re-image from a trusted baseline is necessary.

Known aliases

Threat reports may refer to this family under multiple names:

• Trojan.MSIL
• MSIL.Bot
• Win32/MSIL.Agent

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

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

• T1059: Restrict execution of scripting languages such as PowerShell, VBScript, or Python to authorized administrators. Enforce Script Block Logging.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

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:

rule MALWARE_WIN_MSILBOT_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Msilbot"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "msilbot" ascii wide nocase
        $s2 = "trojan.msil" ascii wide nocase
        $s3 = "msil.bot" ascii wide nocase
        $s4 = "win32/msil.agent" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Msilbot (Ransomware) Execution & Triage
id: 9d2668b4-9feb-5d23-85e1-de027cb2fdd3
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Msilbot malware family. Detects volume shadow copy deletion, boot status
  tampering, and recovery inhibition characteristic of modern ransomware operations.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/msilbot
- 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.ransomware
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1059
- attack.t1105
- attack.t1071_001
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \vssadmin.exe
    - \wmic.exe
    - \wbadmin.exe
    - \bcdedit.exe
    CommandLine|contains:
    - delete shadows
    - shadowcopy delete
    - resize shadowstorage
    - recoveryenabled no
    - ignoreallfailures
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: critical

rule MALWARE_WIN_MSILBOT_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Msilbot 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 = "msilbot" 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
}

Containment & Response Steps

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

1. Immediately isolate affected host(s) from the internal network (disconnect physical Ethernet and disable Wi-Fi/Bluetooth) to prevent Msilbot from spreading laterally or encrypting network-attached storage (NAS) and shared SMB volumes.
2. Preserve volatile system memory (RAM capture) on a representative endpoint before attempting a reboot or power-down, as Msilbot symmetric encryption keys or uncompiled payload components may still reside in memory.
3. Audit process execution logs and terminate active scripting interpreters (e.g. PowerShell, CMD, WScript) or commands executing 'vssadmin.exe delete shadows' or 'wbadmin' used by Msilbot to inhibit recovery.
4. Investigate the initial compromise vector (such as exposed RDP instances, spearphishing attachments, or vulnerable edge gateways) and enforce an immediate credential reset for all compromised Active Directory accounts.
5. Restore critical assets and databases exclusively from verified, air-gapped, or immutable offline backups once the Msilbot binary and related persistence hooks are eradicated.

What to Avoid

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

1. Do not restart or power cycle infected systems prematurely; doing so destroys volatile RAM encryption keys and may trigger bootloader locking logic embedded in Msilbot.
2. Avoid negotiating or paying the extortion demand without prior forensic evaluation and consultation with incident response specialists, as payment does not guarantee data recovery.
3. Do not connect clean backup drives or external storage to the affected network until Msilbot eradication is completely verified.

References & External Analysis

• Search "msilbot" on VirusTotal (External Analysis)
• Search "msilbot" on Any.Run (Sandbox Sandbox)
• Search "msilbot" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Ransomware)

Explore other documented threats in the same operational category:

• Fosniw
• Cobra
• Sisron
• Clhf
• Flvdirect
• Winemm
• Genericrxfo
• Mdrop

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/msilbot.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.