Today we’re speaking with Rupert Marais, our in-house security specialist, about a series of newly disclosed techniques that turn the humble Windows shortcut, or LNK file, into a surprisingly potent tool for cyberattacks. We’ll be exploring the technical nuances of how these shortcuts can be manipulated to deceive users and execute malicious code, examining the ongoing debate about what constitutes a security vulnerability, and discussing what both end-users and security teams can do to defend against this evolving threat.
You’ve found that manipulating a shortcut’s EnvironmentVariableDataBlock can display a fake target like “invoice.pdf” while executing PowerShell. Could you walk me through the technical steps of how this spoofing works and why it is so effective at hiding malicious commands from a user?
It’s a remarkably deceptive technique that preys on how Windows Explorer handles inconsistencies within the LNK file format. At its core, the exploit involves manipulating two specific fields within the file’s data structures: the ANSI target field and the Unicode target field inside the EnvironmentVariableDataBlock. An attacker can carefully craft a shortcut where they populate the ANSI field with a malicious command, like a PowerShell script, but intentionally leave the Unicode field empty. When a user inspects the shortcut’s properties, Windows Explorer gets confused and instead displays information from a different data structure, the LinkTargetIDList, which the attacker has set to something benign, like “invoice.pdf.” The deception is nearly perfect because not only is the displayed target completely spoofed, but any command-line arguments are also hidden, making visual inspection feel reassuringly safe while the malicious payload executes the moment you double-click.
When presented with these LNK file issues, Microsoft stated they do not meet the bar for a vulnerability because they require user interaction. How does this classification contrast with the response to similar exploits like CVE-2025-9491, and what does this imply about security boundary definitions?
This is where the line gets incredibly blurry and, frankly, a bit concerning. Microsoft’s official stance is that because a user must be tricked into clicking the file, it doesn’t cross a “security boundary” on its own. However, this feels inconsistent when you look at the history of a very similar flaw, CVE-2025-9491. Initially, Microsoft gave the same justification for not fixing it, yet they later silently patched the issue in June 2025. Why the change of heart? Because that vulnerability was being actively and widely exploited by at least 11 different state-sponsored and cybercrime groups, from Evil Corp to Mustang Panda. The reality on the ground is that threat actors live in this gray area. They know users can be tricked, and saying it’s not a “true” vulnerability because it requires social engineering ignores the fact that this is how modern attacks succeed. It suggests the definition of a security boundary is more of a philosophical line than a practical one that reflects real-world attack chains.
Attackers can use invalid path characters or conflicting data structures to make a shortcut’s displayed target different from its executed one. From a user’s perspective, what visual red flags might appear, and what practical steps can a cautious employee take to verify a shortcut’s true destination?
From a user’s perspective, this is a nightmare scenario because the very tools you would use to verify a file are being turned against you. The properties dialog, which should be a source of truth, is lying. You might see a target path like “C:\Docs\invoice.pdf,” and it looks completely legitimate, but that’s not what runs. There are almost no reliable visual red flags. The most practical step isn’t to trust what you see, but to question where the file came from. Did you expect this file from this sender? Is there a legitimate business reason for receiving a shortcut instead of the file itself? My advice is to treat all unsolicited LNK files with extreme prejudice. Heed the security warnings that Windows does display for files downloaded from the internet. It’s that one moment of hesitation—that split second of questioning the source—that can make all the difference, because you can’t trust the file’s appearance.
The exploit relies on Windows Explorer forgivingly interpreting malformed LNK files instead of rejecting them. What are the trade-offs for Microsoft in maintaining this backward compatibility, and what technical changes could be implemented to validate these files more strictly without breaking legitimate functionality?
The trade-off is a classic one: compatibility versus security. The LNK file format has been around since Windows 95, and over decades of different operating systems and applications, countless shortcuts have been created. Microsoft’s “forgiving” interpretation is designed to ensure that older or slightly non-standard, but legitimate, shortcuts don’t suddenly break after a system update. To them, rejecting a malformed file that might be legitimate is a bigger user-experience problem than allowing a cleverly crafted malicious one to be interpreted. However, technical changes are certainly possible. A more stringent validation process could be implemented where Explorer checks for consistency. For instance, it could enforce a rule that if multiple data structures within the LNK file define a target path, they must all match. If there’s a conflict between the LinkInfo field and the LinkTargetIDList, the file should be flagged as invalid or at least trigger a much more severe security warning, rather than silently choosing one path to display and another to execute.
Beyond standard security warnings, which users often click through, what specific detection rules or endpoint behaviors should security teams monitor to proactively identify these deceptive LNK files in their environment? Please provide a few examples of indicators of compromise.
Security teams need to look beyond the surface, as user-based warnings are simply not enough. A great indicator of compromise to hunt for is an LNK file that contains data in the EnvironmentVariableDataBlock’s target field while the corresponding Unicode field is empty or mismatched—this is a hallmark of the most potent spoofing technique. Another rule would be to flag any LNK files that use forbidden path characters, like double quotes, within the target field, as this is a known method for confusing the parser. On the endpoint, monitor for processes like PowerShell, CMD, or MSHTA being spawned by explorer.exe immediately after a user opens an LNK file, especially if that shortcut purports to be a simple document. This parent-child process relationship is highly suspicious and often points directly to a malicious shortcut in action.
What is your forecast for the use of LNK files in cyberattacks?
I believe we are going to see a significant and sustained increase in the use of malicious LNK files. The barrier to entry for attackers is being lowered by the release of open-source tools that can generate these deceptive files, and their effectiveness is undeniable. As long as threat actors, from sophisticated state-backed groups like those in China and North Korea to common cybercrime gangs, see success with these methods, they will continue to refine and deploy them. Because Microsoft has classified these techniques as outside the scope of immediate security servicing, attackers now have a stable, unpatched attack vector they can rely on. Until there is a fundamental shift in how the operating system parses these files, LNK shortcuts will remain a favorite tool for initial access, allowing attackers to bypass simple file-type blocks and trick even cautious users into executing their malicious code.
