{
  "family": "msilpack",
  "sample_count": 1,
  "category": "advanced_threat",
  "description": "<h3>Executive Summary</h3>\nMSILPack (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.\n\n<h3>Technical Capabilities and Evasion</h3>\nAn MSILPack detection does not indicate a specific malware family; rather, it indicates the <em>method</em> used to hide the true malware. .NET applications are easily decompiled, so attackers use these packers to encrypt the core malicious logic.\n\nWhen an MSILPack executable is run, it performs a complex \"unpacking\" routine entirely in memory:\n<ul>\n<li><strong>Memory Decryption:</strong> 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.</li>\n<li><strong>Process Hollowing / RunPE:</strong> 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.</li>\n<li><strong>Payload Execution:</strong> 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.</li>\n</ul>\n\n<h3>Threat Assessment</h3>\nThe 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.\n\n<h3>Incident Response and Remediation</h3>\n<ul>\n<li><strong>Behavioral Analysis (EDR):</strong> 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.</li>\n<li><strong>Network Isolation and Triage:</strong> Isolate the machine immediately. Analyze network traffic to identify the C2 server the injected process is communicating with.</li>\n<li><strong>Assume Credential Compromise:</strong> 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.</li>\n</ul>",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [
    "Trojan.MSIL.Packer",
    "MSIL/Cryptor",
    "Win32/MSILPack"
  ],
  "enrichment_level": "insufficient_information",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1027.002",
    "T1055.002",
    "T1055.012"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-07-01T17:46:29Z",
  "type": "Generic MSIL Packer / Obfuscator",
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}