{
  "family": "multijoiner",
  "sample_count": 1,
  "category": "trojan",
  "description": "<h3>Executive Summary</h3>\nMultiJoiner is a specialized \"HackTool\" and utility program designed specifically for malicious file bundling. Also known as a \"binder\" or \"joiner,\" it allows threat actors to take a malicious executable (like a Trojan or RAT) and silently fuse it with a legitimate, benign file (such as a PDF, a JPG image, or a software installer). When the victim opens the seemingly safe file, the malicious payload is executed invisibly in the background.\n\n<h3>Infection Vector and Technical Capabilities</h3>\nMultiJoiner itself is the tool used to *create* the infection vector. Files bound by MultiJoiner are typically distributed via targeted spear-phishing (e.g., an email with an \"Invoice.pdf.exe\" disguised using right-to-left override characters) or shared on peer-to-peer networks masquerading as cracked software.\n\nUpon execution of the \"joined\" file, the following sequence occurs:\n<ul>\n<li><strong>Silent Extraction:</strong> The hidden stub code generated by MultiJoiner extracts both the legitimate file and the malicious payload to a temporary directory (e.g., `%TEMP%` or `%APPDATA%`).</li>\n<li><strong>Simultaneous Execution:</strong> The utility executes the legitimate file (e.g., opening the PDF in Adobe Reader) so the user suspects nothing, while simultaneously executing the malware in the background.</li>\n<li><strong>Icon and Extension Spoofing:</strong> MultiJoiner allows the attacker to steal the icon of the legitimate file (e.g., applying a PDF icon to the final `.exe`) to further deceive the victim into clicking the executable.</li>\n</ul>\n\n<h3>Threat Assessment</h3>\nThe detection of a tool like MultiJoiner on a corporate network is a severe indicator of internal malicious activity, strongly suggesting a compromised developer workstation or an active insider threat attempting to weaponize payloads for internal deployment. If a file *created* by MultiJoiner is detected, it signifies a highly deceptive social engineering attack has bypassed initial perimeter filters.\n\n<h3>Incident Response and Remediation</h3>\n<ul>\n<li><strong>Investigate the Source:</strong> If the MultiJoiner application itself is found, immediately isolate the machine and investigate the user's activities. Determine what files were bound and where they were distributed.</li>\n<li><strong>Forensic Unbundling:</strong> If a joined file is detected, do not execute it. Security analysts must extract the malicious payload from the binder to analyze its true intent (e.g., identifying C2 servers or payload types).</li>\n<li><strong>User Awareness Training:</strong> The effectiveness of bound files relies entirely on users double-clicking executables disguised as documents. Reinforce training regarding hidden file extensions and suspicious attachments.</li>\n</ul>",
  "cta": "Published by the SystemHelpdesk team.",
  "aliases": [
    "HackTool.MultiJoiner",
    "Binder.MultiJoiner",
    "Win32/Joiner"
  ],
  "enrichment_level": "insufficient_information",
  "faq": [],
  "faq_count": 0,
  "mitre_attack": [
    "T1027",
    "T1036.004",
    "T1204.002"
  ],
  "cisa_advisory": null,
  "last_updated": "2026-07-02T07:05:10Z",
  "type": "HackTool / Binder",
  "target_industries": [
    "Global / Opportunistic"
  ],
  "motivation": "Opportunistic",
  "threat_actors": [
    "Unknown / Cybercriminal"
  ],
  "target_geographies": [
    "Global"
  ]
}