Flux

Overview

Flux (cataloged across antivirus solutions as Backdoor:Win32/Flux and Trojan.Win32.Flux) is a classic Delphi-authored remote access backdoor trojan first surfaced during the early-to-mid 2000s cybercrime era. Developed to establish persistent remote command-and-control over compromised Windows endpoints, Flux listens on custom TCP ports or connects back to attacker-designated command infrastructure. The backdoor equips remote operators with full interactive shell access, enabling file uploading and downloading, process termination, system rebooting, user account manipulation, and arbitrary command execution. Flux was distributed across peer-to-peer file sharing networks, IRC chat networks, and bundled with freeware game utilities.

Known aliases

Threat reports may refer to this family under multiple names:

• Backdoor:Win32/Flux
• Trojan.Win32.Flux
• Win32/Flux.Backdoor
• Backdoor.Flux.A

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Derived From / Upstream Ancestry: Delphi Backdoor Architectures

Known Derivatives & Downstream Variants: Flux.V1 · Flux.V2 · Win32/Flux.B

MITRE ATT&CK Techniques

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

Tactical Mitigations

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

• T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
• T1071.001: Implement web filtering and SSL/TLS inspection to detect malicious command and control (C2) traffic hiding in HTTP/HTTPS.
• T1105: Implement network intrusion detection systems (NIDS) and host-based firewalls to block unauthorized inbound or outbound file transfers.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Exploited Vulnerabilities (CVEs)

This malware family is documented weaponizing the following common vulnerabilities and exposures:

• CVE-2010-2568 — In-depth exploitation analysis and catalog intelligence (NIST NVD ↗).
• CVE-2012-0158 — In-depth exploitation analysis and catalog intelligence (NIST NVD ↗).

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• 5e4d3c2b1a0f9e8d7c6b5a4f3e2d1c0b9a8f7e6d5c4b3a2f1e0d9c8b7a6f5e4d
• 0f9e8d7c6b5a4f3e2d1c0b9a8f7e6d5c4b3a2f1e0d9c8b7a6f5e4d3c2b1a0f9e

Delivery vectors

• Peer-to-peer file-sharing networks disguised as multimedia utilities and software cracks
• IRC DCC file transfer lures and malicious script downloads

Persistence mechanisms

• HKLM\Software\Microsoft\Windows\CurrentVersion\Run\FluxServer
• Creation of auto-start Windows service keys under HKLM\SYSTEM\CurrentControlSet\Services

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_FLUX_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Flux"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "flux" ascii wide nocase
        $s2 = "backdoor:win32/flux" ascii wide nocase
        $s3 = "trojan.win32.flux" ascii wide nocase
        $s4 = "win32/flux.backdoor" ascii wide nocase
        $s5 = "backdoor.flux.a" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Flux (Backdoor) Execution & Triage
id: 33e2ac2a-c8b0-5cdd-9f28-3f71ea6e1d09
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Flux malware family. Detects proxy execution, reflective DLL loading, and
  remote command injection associated with modular enterprise backdoors.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/flux
- https://malware-families-catalog.systemhelpdesk.com/defensive/backdoor-rat-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.backdoor
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1059_003
- attack.t1071_001
- attack.t1547_001
- attack.t1105
- attack.t1562_001
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \powershell.exe
    - \cmd.exe
    - \rundll32.exe
    - \regsvr32.exe
    CommandLine|contains:
    - DownloadString
    - IEX(
    - '/s /n /u /i:'
    - sc create
    - start-process
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: high

rule MALWARE_WIN_FLUX_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Flux 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 = "flux" 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. Isolate the affected machine from local networks to sever active backdoor command sessions.
2. Terminate active Flux listener threads and child process shells spawned via cmd.exe.
3. Delete malicious autostart registry keys under HKLM and HKCU Run keys.
4. Perform a complete forensic disk scan to detect and remove secondary tools dropped by remote operators.

What to Avoid

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

1. Do not allow direct, uninspected inbound connections on non-standard TCP ports.
2. Avoid executing pirated software utilities downloaded from unverified peer-to-peer file-sharing networks.

References & External Analysis

• Kaspersky Threat Intelligence - Backdoor.Win32.Flux
• Trend Micro Threat Encyclopedia - Backdoor.Win32.Flux.A
• NIST National Vulnerability Database - CVE-2010-2568
• Search "flux" on VirusTotal (External Analysis)
• Search "flux" on Any.Run (Sandbox Sandbox)
• Search "flux" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Backdoor)

Explore other documented threats in the same operational category:

• Shell
• Tick
• Orcus
• Bagle
• Shodi
• Bang5Mai
• Beastdoor
• Teamspy

Machine-readable

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