Cryptxxx

Overview

Ransom:Win32/Cryptxxx (also known as UltraCrypter) is a highly destructive, multi-faceted malware family. Unlike simple ransomware that only encrypts files, Cryptxxx acts as a dual-threat: it operates as a severe information stealer (`T1552`) to harvest Bitcoin wallets and passwords *before* it begins its cryptographic attack (`T1486`). This ensures the attackers can monetize the infection even if the victim refuses to pay the ransom.

Understanding Cryptxxx (Dual-Threat Ransomware)
To an end-user, the impact is catastrophic: personal files are locked with a `.crypt` or `.crypz` extension, a ransom note demands payment, and they may later find their cryptocurrency wallets drained. For a SOC analyst, Cryptxxx represents a massive breach of confidentiality and availability. It was heavily distributed by the Angler and Neutrino Exploit Kits.

Execution and Extortion Mechanics
Upon execution, Cryptxxx first establishes persistence (often copying itself to `%AppData%` and modifying the `Run` registry key). Before encrypting anything, it scans the hard drive for Bitcoin wallet files (`wallet.dat`), FTP credentials, email passwords, and browser cookies, exfiltrating this data to its C2 server (`T1041`). Once exfiltration is complete, it begins a rapid encryption routine using RSA-4096 and AES-256 (`T1486`). It actively attempts to delete Volume Shadow Copies (`T1490`) using `vssadmin.exe` to thwart recovery efforts.

Indicators of Compromise & Impact
The impact is total data loss and severe credential compromise. Host-based IoCs include the presence of files appended with `.crypt`, `.crypz`, or `.crypt1`. Ransom notes are typically dropped as `de_crypt_readme.txt` or `de_crypt_readme.html`. EDR tools will flag the execution of `vssadmin.exe delete shadows /all /quiet`. Network IoCs include initial exfiltration traffic (often over non-standard ports) followed by Tor-based C2 communication.

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_CRYPTXXX {
    meta:
        description = "Detects Cryptxxx (ransomware)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "cryptxxx" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Cryptxxx Activity
id: 29bd3e3ef2b2a203ca3d5ed409fbcbba
status: experimental
description: Detects generic indicators of the cryptxxx malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*cryptxxx*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Isolate the infected endpoint IMMEDIATELY by physically disconnecting the network cable to halt the exfiltration of credentials and the encryption of network shares.
2. Assume all passwords and cryptocurrency wallets stored on the machine are compromised; force immediate password resets from a clean machine.
3. Check NoMoreRansom.org; flaws in earlier versions of Cryptxxx allowed security researchers to release free decryption tools.
4. Restore the encrypted files from an offline, secure backup.

What to Avoid

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

1. Do not pay the ransom; paying funds criminal enterprises, and free decryptors exist for many variants of Cryptxxx.
2. Do not assume that removing the ransomware solves the problem; you must address the stolen credentials.

References & External Analysis

• Search "cryptxxx" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: ransomware)

Explore other malware families in the same category:

• Remas
• Xxybtw
• Gatak
• Mudrop
• Jord

Machine-readable

Get this profile as JSON: https://jordanricky1604-ship-it.github.io/malware-families-catalog/api/cryptxxx.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.