Flymux

Overview

Executive Summary

Infection Vector and Technical Capabilities

• Browser and Email Harvesting: The malware actively scans the registry and local AppData folders to extract saved passwords, autofill data, and session cookies from major web browsers (Chrome, Firefox, Internet Explorer). It also targets email clients (Outlook, Thunderbird).
• FTP/Webmaster Targeting: Flymux frequently hunts for configuration files and saved passwords associated with popular FTP clients (like FileZilla or WinSCP). Stolen FTP credentials allow the attacker to deface websites or host further malware payloads.
• Data Exfiltration: Once the data is harvested, Flymux encrypts the stolen information and transmits it to an attacker-controlled server via HTTP POST requests, completing its execution quickly to evade prolonged detection.

Threat Assessment

Incident Response and Remediation

• MFA Token Revocation: Assume session cookies were stolen. Force an immediate sign-out of all active sessions for critical web applications to invalidate the stolen tokens.
• Local Password Reset: All user credentials saved in the affected endpoint's web browsers, email clients, and FTP software must be considered compromised and reset from a clean device.
• Endpoint Eradication: The malware itself is typically not heavily obfuscated and can often be removed by a reputable EDR or enterprise antivirus solution. Ensure a full system scan is completed to verify eradication.

Known aliases

Threat reports may refer to this family under multiple names:

• Trojan.Flymux
• PWS.Flymux
• TrojanSpy.Flymux

MITRE ATT&CK Techniques

This family has been observed using the following ATT&CK techniques: T1555.003 T1539 T1056.001 T1048

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.

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_FLYMUX {
    meta:
        description = "Detects Flymux (advanced_threat)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "flymux" ascii wide nocase
        $s2 = "trojan.flymux" ascii wide nocase
        $s3 = "pws.flymux" ascii wide nocase
        $s4 = "trojanspy.flymux" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Flymux Activity
id: 8a993d6d1517b788d3bf496a8dcc5e7f
status: experimental
description: Detects generic indicators of the flymux malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*flymux*"
            - "*trojan.flymux*"
            - "*pws.flymux*"
            - "*trojanspy.flymux*"
    condition: selection
level: medium

References & External Analysis

• Search "flymux" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Qqfarmassist
• Familykeylogger
• Dotbundle
• Advpassman
• Speed

Machine-readable

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