Tsklnk

Overview

Trojan:Win32/Tsklnk (Task Link) is a specific classification for malware that abuses legitimate Windows Shortcut files (`.lnk`) and the Windows Task Scheduler to establish highly evasive persistence and execute malicious payloads. It is often a component of a larger infection chain, heavily utilized by fileless malware and USB-spreading worms to execute PowerShell or VBScript without leaving a traditional executable on the disk.

Understanding Tsklnk (Malicious LNKs)
To an end-user, Tsklnk often appears as a benign icon (like a folder or a PDF document) on a USB drive or the desktop. When double-clicked, the icon might briefly flash a command prompt before opening the expected document, masking the malicious activity. For a security analyst, Tsklnk represents an abuse of fundamental Windows OS features (Living off the Land). Because `.lnk` files and Scheduled Tasks are native, administrative tools, they often bypass traditional antivirus scans.

Execution and Persistence Mechanics
Tsklnk is frequently delivered via phishing (as an attached `.lnk` disguised as a document) (`T1566.002`) or via infected USB drives (`T1091`). The core of the threat lies in the 'Target' property of the Shortcut file. Instead of pointing to an application, the `.lnk` file executes `cmd.exe` or `powershell.exe` (`T1059.003`), passing it an obfuscated, base64-encoded command line (`T1027`). This command often reaches out to a C2 server to download and execute a secondary payload entirely in memory (`T1105`). To achieve persistence, the malware creates a hidden Scheduled Task (`T1053.005`) that points to a similarly malicious `.lnk` file or directly executes a PowerShell one-liner every time the user logs in.

Indicators of Compromise & Impact
The impact is a stealthy, persistent backdoor. Host-based IoCs include EDR alerts for `cmd.exe` or `powershell.exe` being spawned by `explorer.exe` (when the user clicks the shortcut) with exceptionally long, encoded command-line arguments. The presence of anomalous Scheduled Tasks executing scripts or binaries from temporary directories, and `.lnk` files on USB drives with targets pointing to `cmd.exe` rather than an application, are definitive IoCs.

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.
• T1566.002: Inspect email links for known malicious domains and use link-rewriting services for time-of-click analysis.

MITRE D3FEND™ Defensive Countermeasures

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

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_TSKLNK_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Tsklnk"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "tsklnk" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Tsklnk (Trojan) Execution & Triage
id: 7d72b390-c774-5954-ba6c-76049b574a54
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Tsklnk 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/tsklnk
- 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.t1204_002
- attack.t1059_003
- attack.t1053_005
- attack.t1566_002
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_TSKLNK_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Tsklnk 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 = "tsklnk" 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. Audit the Windows Task Scheduler across the affected endpoints, looking for tasks with suspicious triggers (e.g., 'At Logon') and actions executing `powershell.exe` or `cmd.exe` with encoded arguments.
2. Use EDR to hunt for process execution events where the command line contains strings like `-ExecutionPolicy Bypass`, `-WindowStyle Hidden`, or base64 encoding (`-enc`, `-EncodedCommand`).
3. Disable Windows AutoRun/AutoPlay to prevent LNK files on USB drives from executing automatically.
4. Delete the malicious `.lnk` files and the scheduled tasks they created.

What to Avoid

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

1. Do not assume the system is clean just because an antivirus scan removed a dropped executable; Tsklnk often operates 'filelessly' via the registry and scheduled tasks.
2. Avoid interacting with suspicious shortcut files manually on a live system; analyze the LNK file properties using specialized forensic tools (like LEC) in an isolated environment.

References & External Analysis

• Search "tsklnk" on VirusTotal (External Analysis)
• Search "tsklnk" on Any.Run (Sandbox Sandbox)
• Search "tsklnk" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Trojan)

Explore other documented threats in the same operational category:

• Bankfraud
• Travnet
• Seznam
• Pcreviver
• Hideproc
• Browshot
• Findkeyxp
• Corebot

Machine-readable

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