{ "family": "klozet", "sample_count": 1, "category": "ransomware", "description": "

Executive Summary

\nKlozet is a malicious Trojan designed to covertly infiltrate Windows systems, establish persistence, and act as a reliable downloader for remote threat actors. It is frequently utilized in the initial stages of a cyberattack to gather system intelligence and facilitate the automated deployment of secondary, more destructive malware payloads.\n\n

Infection Vector and Technical Capabilities

\nKlozet is predominantly distributed through socially engineered spam campaigns containing malicious attachments (often weaponized PDFs or Office documents) or via compromised software installers.\n\nUpon successful execution, Klozet operates with a focus on stealth and payload delivery:\n\n\n

Threat Assessment

\nA Klozet infection represents a significant breach of the endpoint perimeter. Because it provides remote attackers with the ability to execute arbitrary code, a compromised machine can quickly be utilized to pivot laterally across the corporate network or be fully encrypted by a secondary ransomware payload.\n\n

Remediation and Eradication

\n", "cta": "Published by the SystemHelpdesk team.", "aliases": [ "Trojan.Klozet", "Downloader.Klozet", "Win32/Klozet" ], "enrichment_level": "expert-seo", "faq": [ { "@type": "Question", "name": "What is Klozet and what threat category does it belong to?", "acceptedAnswer": { "@type": "Answer", "text": "Klozet is classified as a Ransomware. Documented across security telemetry, it is engineered to execute unauthorized operations, establish persistent footholds on target endpoints, and facilitate malicious campaigns targeting enterprise and individual environments." } }, { "@type": "Question", "name": "How does Klozet establish persistence and evade defensive controls?", "acceptedAnswer": { "@type": "Answer", "text": "Klozet typically establishes persistence through registry run keys, scheduled tasks, or service installations, while evading signature-based antivirus solutions through code obfuscation, memory injection, or anti-analysis sandbox checks." } }, { "@type": "Question", "name": "What are the essential incident response steps for mitigating a Klozet compromise?", "acceptedAnswer": { "@type": "Answer", "text": "Security teams responding to Klozet should immediately isolate affected endpoints from the network, perform memory triage to capture volatile forensic artifacts, audit registry and startup persistence mechanisms, revoke exposed user credentials, and restore systems from verified, clean backups." } }, { "@type": "Question", "name": "What cryptographic algorithms and file targeting techniques does Trojan.Klozet employ during execution?", "acceptedAnswer": { "@type": "Answer", "text": "Trojan.Klozet typically leverages hybrid cryptographic architectures combining symmetric stream or block ciphers (such as AES-256 or ChaCha20) for rapid file encryption with asymmetric algorithms (such as RSA-2048 or Curve25519) to securely protect the session keys. It aggressively targets sensitive file extensions including corporate documents, databases, virtual disks, and backups while systematically executing commands to delete Volume Shadow Copies (vssadmin delete shadows /all /quiet) and disable system recovery options." } }, { "@type": "Question", "name": "Are decryptors available for Trojan.Klozet, and what is the recommended recovery procedure?", "acceptedAnswer": { "@type": "Answer", "text": "Decryption availability for Trojan.Klozet depends on whether security researchers or law enforcement (such as the No More Ransom initiative) have recovered the master private keys or discovered flaws in its key generation routines. Victims should never pay the extortion demand, as payment fuels criminal operations without guaranteeing file restoration. The recommended recovery procedure entails isolating infected hosts, conducting forensic disk imaging, identifying the root access vector, and restoring validated systems from immutable offline backups." } } ], "faq_count": 5, "mitre_attack": [ "T1105", "T1547.001", "T1059" ], "cisa_advisory": null, "last_updated": "2026-10-15", "type": "Trojan", "target_industries": [ "Healthcare", "Critical Infrastructure", "Enterprise" ], "motivation": "Financial Extortion", "threat_actors": [ "Unknown / Cybercriminal" ], "target_geographies": [ "Global" ], "attack_stage": [ "defense_evasion", "impact" ], "ecosystem": [ "windows_pe" ], "is_emerging": false, "mitre_attack_detail": [ { "id": "T1105", "name": "Ingress Tool Transfer", "tactic": "Command and Control" }, { "id": "T1547.001", "name": "Boot or Logon Autostart Execution: Registry Run Keys / Startup Folder", "tactic": "Persistence" }, { "id": "T1059", "name": "Command and Scripting Interpreter", "tactic": "Execution" } ], "containment_steps": [ "Immediately isolate affected host(s) from the internal network (disconnect physical Ethernet and disable Wi-Fi/Bluetooth) to prevent Klozet from spreading laterally or encrypting network-attached storage (NAS) and shared SMB volumes.", "Preserve volatile system memory (RAM capture) on a representative endpoint before attempting a reboot or power-down, as Klozet symmetric encryption keys or uncompiled payload components may still reside in memory.", "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 Klozet to inhibit recovery.", "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.", "Restore critical assets and databases exclusively from verified, air-gapped, or immutable offline backups once the Klozet binary and related persistence hooks are eradicated." ], "what_to_avoid": [ "Do not restart or power cycle infected systems prematurely; doing so destroys volatile RAM encryption keys and may trigger bootloader locking logic embedded in Klozet.", "Avoid negotiating or paying the extortion demand without prior forensic evaluation and consultation with incident response specialists, as payment does not guarantee data recovery.", "Do not connect clean backup drives or external storage to the affected network until Klozet eradication is completely verified." ], "target_platforms": [ "Windows 11", "Windows 10", "Windows Server 2022", "Windows Server 2019" ] }