Uk_Splitter

Overview

UK Splitter (specifically known across security communities as UK Splitter 1.2 and HackTool.Win32.UKSplitter) is a specialized binary joiner, executable file binder, and malware dropper companion created circa 2003 by a hacker group known as 'UK-Crew'. Widely utilized in underground cybercrime circles, UK Splitter was designed to merge malicious backdoor servers (such as SubSeven, NetBus, or Optix Pro) with benign host programs (such as games, media players, or images). When the victim executes the bound carrier file, UK Splitter extracts and displays the legitimate decoy program in the foreground to eliminate suspicion, while simultaneously dropping and executing the malicious payload silently in the background. UK Splitter featured customizable executable icon replacement, stub compression, and automated autostart registry configuration to ensure persistent execution across system reboots.

Known aliases

Threat reports may refer to this family under multiple names:

• UK Splitter 1.2
• HackTool.Win32.UKSplitter
• Binder.UKSplitter
• UK Splitter Pro
• UK-Crew Splitter

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: Win32 Binary Joiners And Droppers

Known Derivatives & Downstream Variants: Uk Splitter 1.0 · Uk Splitter 1.2 · Uk Splitter Pro

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:

• T1036.005: Monitor for executable files running from unusual paths or with deceptive names. Use EDR to detect process masquerading.
• T1059.003: Restrict execution of Windows Command Shell (cmd.exe) and block unauthorized batch scripts.
• 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):

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.

• b1c2d3e4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2
• 5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b2c3d4e5f6a

Delivery vectors

• Trojanized freeware software downloads and pirated game archives distributed via P2P
• Email attachments disguised as legitimate multimedia files or PDF documents

Persistence mechanisms

• HKCU\Software\Microsoft\Windows\CurrentVersion\Run\UKSplitterStub
• %TEMP%\dropped_server.exe

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_UK_SPLITTER_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Uk_Splitter"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "uk_splitter" ascii wide nocase
        $s2 = "uk splitter 1.2" ascii wide nocase
        $s3 = "hacktool.win32.uksplitter" ascii wide nocase
        $s4 = "binder.uksplitter" ascii wide nocase
        $s5 = "uk splitter pro" ascii wide nocase
        $s6 = "uk-crew splitter" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Uk_splitter (Trojan) Execution & Triage
id: b192a872-2054-57c5-8ff1-e106c248fba3
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Uk_splitter malware family. Detects suspicious execution from temporary
  user directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/uk_splitter
- https://malware-families-catalog.systemhelpdesk.com/defensive/downloader-dropper-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.trojan
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1027_002
- attack.t1036_005
- attack.t1105
- attack.t1059_003
- attack.t1547_001
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \cscript.exe
    - \wscript.exe
    CommandLine|contains:
    - AppData\Local\Temp
    - -WindowStyle Hidden
    - /e:jscript
    - bitsadmin /transfer
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: medium

rule MALWARE_WIN_UK_SPLITTER_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Uk_Splitter 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 = "uk_splitter" 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. Terminate both the decoy application and the secondary dropped payload executing from %TEMP% or %APPDATA%.
2. Delete the extracted malicious binaries and bound carrier executables.
3. Remove startup keys under HKCU\Software\Microsoft\Windows\CurrentVersion\Run created by the dropped payload.
4. Run a full antimalware scan to ensure no additional payloads were dropped onto the system.

What to Avoid

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

1. Do not execute software files downloaded from unverified forums, P2P networks, or file sharing sites.
2. Avoid bypassing operating system executable signing checks when opening third-party files.

References & External Analysis

• Trend Micro Threat Encyclopedia - HackTool.Win32.UKSplitter
• Malware Museum Historical Binder Collection - UK Splitter
• Search "uk_splitter" on VirusTotal (External Analysis)
• Search "uk_splitter" on Any.Run (Sandbox Sandbox)
• Search "uk_splitter" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Netsphere
• Defaulttab
• Yahoopass
• Jacard
• Msilinj
• Anyprotect
• Erazer_Lite
• Strongpity

Machine-readable

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