Chthonic

Overview

Trojan:Win32/Chthonic is an advanced, highly sophisticated Banking Trojan and a direct evolutionary offshoot of the infamous ZeuS (Zbot) malware source code. Discovered around 2014, Chthonic is designed to stealthily hijack online banking sessions, bypass two-factor authentication, and facilitate massive financial fraud utilizing complex web injection techniques and modular architecture.

Understanding Chthonic
To an infected user, Chthonic is entirely invisible. When the user logs into their online bank, everything looks normal. For a threat intelligence analyst, Chthonic represents a top-tier financial threat. It utilizes a modular framework, downloading specific plugins (like a keylogger, a VNC module for remote control, or a video recorder) based on the attacker's needs. Its primary weapon is 'Man-in-the-Browser' (MitB) capabilities, allowing it to modify banking web pages on the fly to trick users into handing over authentication tokens.

Execution and Web Injection Mechanics
Chthonic was typically distributed via the Andromeda botnet or malicious document attachments (`T1566.001`). Upon execution, it utilizes aggressive process injection (`T1055`)—often injecting into `msiexec.exe` or the browser process itself—to establish a foothold and hide from security software. Once a user navigates to a targeted banking URL, Chthonic intercepts the browser's web traffic (`T1185`). Using its web inject configuration file (downloaded from the C2), it seamlessly inserts fake HTML forms (e.g., 'Please verify your ATM PIN') directly into the legitimate banking page (`T1056.002`). It captures the user's keystrokes, credentials, and answers to security questions, exfiltrating the data to the attacker's server to automate fraudulent wire transfers.

Indicators of Compromise & Impact
The impact is severe financial loss, often bypassing modern security controls like SMS tokens. Incident responders will rarely see obvious signs of infection. EDR platforms must alert on process hollowing or suspicious memory injections targeting `explorer.exe` or web browser executables (Chrome, Firefox, IE). Memory forensics is required to extract the unencrypted Chthonic configuration file, which reveals the specific banks being targeted.

MITRE ATT&CK Techniques

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

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1056.001: Implement Endpoint Detection and Response (EDR) to monitor for suspicious API calls related to keystroke interception. Enforce Multi-Factor Authentication (MFA) to render stolen passwords useless.
• T1056.002: Monitor for unauthorized keylogging, screen capturing, or web browser API hooking. Deploy EDR to detect API hooking.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.
• T1185: Enforce strong MFA and use browser isolation or hardened browsers for sensitive financial or administrative portals to defeat session hijacking.

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_CHTHONIC {
    meta:
        description = "Detects Chthonic (trojan)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "chthonic" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Chthonic Activity
id: 0b093bf1f1d4d924e7fcd6aae2dde6fc
status: experimental
description: Detects generic indicators of the chthonic malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*chthonic*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Instantly isolate the endpoint from the network; an active Chthonic infection means the attacker is likely monitoring banking sessions in real-time.
2. Assume all credentials typed on the machine (corporate passwords, banking logins) are compromised and enforce immediate enterprise-wide password resets.
3. Capture a full forensic memory image (RAM dump) to extract the injected modules and the encrypted web inject configuration file.
4. Do not trust web browsers on the infected machine; perform a complete bare-metal wipe and reinstall of the operating system.

What to Avoid

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

1. Do not assume multi-factor authentication (MFA/SMS) will protect you; Chthonic uses web injects to socially engineer the user into typing the MFA code into a fake prompt.
2. Avoid relying solely on file-based antivirus to 'clean' the infection, as the modular architecture and process hollowing techniques make complete remediation extremely difficult without a format.

References & External Analysis

• Search "chthonic" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: trojan)

Explore other malware families in the same category:

• Mailcheck
• Hotkeyshook
• Proxyweb
• Feebs
• Simbot

Machine-readable

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