LNK Files: A Hidden Windows Security Risk and How to Protect Yourself

Windows shortcut files, known as LNK files, pose a persistent security vulnerability because they can hide malicious instructions from the user’s view. Since Microsoft has yet to patch this core flaw (tracked as CVE-2025-9491), users must take steps to protect their systems from attacks that exploit these shortcuts.

Why LNK Files Are Dangerous

LNK files, identified by the .lnk extensions (which is usually hidden in Windows), are simple shortcuts that point to the location of a file or application. Critically, their target field can also accept command-line arguments and launch instructions. Attackers exploit a vulnerability that allows them to insert empty spaces in this field, hiding malicious scripts beyond the visible limit. The user sees a safe target, but when executed, the shortcut silently runs malware, often used in fileless attacks. A common attack involves hiding a malicious LNK file inside an archive, giving it a deceptive name like “Instructions.pdf” to trick the user into opening it.

Essential Security Measures

To defend against LNK file attacks, the most crucial step is to know you are dealing with a shortcut file. Since LNK files are meant to open files on your PC, receiving one from a third party is a major red flag.

1. Show LNK File Extension: The most important defense is making the .lnk extension visible. Because the default Windows setting doesn’t cover these shortcuts, you need a Registry hack. After backing up your Registry, navigate to HKEY_CLASSES_ROOT\lnkfile and delete the NeverShowExt string. After a restart, all shortcuts will display .lnk, making malicious files easy to identify.
2. Analyze Suspicious LNK Files: If you suspect an LNK file, right-click it, go to Properties, and examine the Target field. A normal shortcut should only contain the path to the app or file. If the target opens a command tool (like cmd.exe or powershell.exe) or contains random characters, binary code, or excessive white space, it is likely malicious.
3. Disable Vulnerable Features: Features historically exploited by LNK attacks, such as AutoPlay for USB drives and the file preview feature in File Explorer, should be disabled. You can turn off AutoPlay in Settings → Bluetooth & devices → AutoPlay, and follow a guide to disable file previews.
4. Enable Controlled Folder Access: This Windows feature protects against ransomware and other tampering by untrusted sources by shielding important user folders (like Documents and Desktop). Since LNK attacks often interact with these folders, enabling Controlled Folder Access adds a valuable layer of security.
5. Harden PowerShell Security: Many LNK attacks use PowerShell commands to execute. You can increase security by restricting PowerShell to only run signed scripts. Open PowerShell as an administrator and run the command: Set-ExecutionPolicy AllSigned. You can undo this change later by running Set-ExecutionPolicy Undefined.

The safest general rule is to never open an LNK file unless you created it yourself or you know the app that created it.