Cryptojoker

Overview

Executive Summary

Infection Vector and Technical Capabilities

• VSS Deletion and Backup Destruction: The ransomware's first action is to execute commands (e.g., `vssadmin.exe Delete Shadows /All /Quiet`) to delete Volume Shadow Copies and disable Windows Recovery, preventing the user from easily restoring the encrypted files.
• Rapid Encryption: It scans local drives and mapped network shares for specific file extensions. It typically uses a combination of AES for fast file encryption and RSA to secure the AES keys. Encrypted files are often appended with a specific extension (e.g., `.joker` or `.crpt`).
• Extortion and Ransom Note: Once encryption is complete, the malware drops a ransom note (usually a `.txt` or `.html` file) in every affected directory and changes the desktop wallpaper. The note provides instructions on how to access a Tor-hosted payment portal to purchase the decryption tool.

Threat Assessment

Incident Response and Remediation

• Immediate Network Severance: The absolute highest priority is to physically sever the infected endpoint (and any servers it can reach) from the network to halt the spread of the encryption across mapped drives and prevent data exfiltration.
• DO NOT REBOOT: Do not reboot the infected machine. Rebooting can trigger "wiper" routines in some ransomware variants or clear volatile memory (RAM) that might contain the encryption key.
• Restore from Offline Backups: Paying the ransom is strongly discouraged, as it funds criminal enterprises and does not guarantee data recovery. Eradication requires a complete bare-metal wipe of the infected infrastructure and a full restoration from secure, offline (air-gapped) backups.

Known aliases

Threat reports may refer to this family under multiple names:

• Ransom.CryptoJoker
• Trojan-Ransom.Win32.CryptoJoker
• Win32/Filecoder.CryptoJoker

MITRE ATT&CK Techniques

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

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_CRYPTOJOKER_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Cryptojoker"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "cryptojoker" ascii wide nocase
        $s2 = "ransom.cryptojoker" ascii wide nocase
        $s3 = "trojan-ransom.win32.cryptojoker" ascii wide nocase
        $s4 = "win32/filecoder.cryptojoker" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Cryptojoker (Ransomware) Execution & Triage
id: bac8268e-40d0-5ef1-8cc4-29b874c07466
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Cryptojoker 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/cryptojoker
- 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.t1486
- attack.t1490
- attack.t1012
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_CRYPTOJOKER_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Cryptojoker 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 = "cryptojoker" 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 Cryptojoker 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 Cryptojoker 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 Cryptojoker 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 Cryptojoker 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 Cryptojoker.
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 Cryptojoker eradication is completely verified.

References & External Analysis

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

Frequently Asked Questions

Related Threats (Category: Ransomware)

Explore other documented threats in the same operational category:

• Pieshua
• Tierry
• Genericrxfo
• Yakbeex
• Spynomore
• Payer
• 5Z0Ba4Mkpih
• Jatif

Machine-readable

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