Internet shortcut files, or so-called URL files, have for years been regarded as harmless and unimportant parts of Windows. However, they are now becoming increasingly used by cybercriminals and APT groups as part of complex infection chains. Thanks to the simplicity of the format, low detection rate and specific system behavior, URL files are becoming silent carriers of malicious code. Experts from OPSWAT are analyzing this new category of threats and providing tools to detect and neutralize them.
Key findings
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URL files are text-based network shortcuts that can initiate multi-stage attacks.
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They are used to run .hta, .js or .cpl payloads, bypass security and leak data.
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These files can act as a phishing attack vector or as part of malware persistence.
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Even advanced APT groups use URL files as low-signal elements in larger campaigns.
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OPSWAT analyzes their structure statically and dynamically using FileTAC and MetaDefender Sandbox.
Table of contents
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What are URL files
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How URL files support cyber attacks
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Why the threat from them is growing
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Strategic use of URL files by APT groups
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How OPSWAT identifies malicious shortcut files
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Summary
What are URL files
A file with the extension .url is a simple INI-formatted Internet shortcut. Its structure is often limited to a single line:
These files allow users to quickly launch a designated website or web application. However, this simplicity is also a potential weakness: the file does not require a signature, it can be easily modified, and launching it activates an external resource.
How URL files support cyber attacks
Today, URL files are increasingly used as:
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Phishing vectors – a user clicks on a shortcut that opens a malicious site or downloads a payload
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Next-stage loaders – e.g., to run .hta or .js remotely
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Security circumvention tools – e.g., bypass SmartScreen and MOTW tag.
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Data leakage mechanisms – e.g., via an icon from SMB or C&C beaconing
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Threat persistence elements – placed in autostart folders
Although seemingly harmless, URL files can be part of a fully developed attack.
Why the threat from them is growing
From a URL file cybersecurity perspective, the threat comes from the fact that:
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These files are commonly ignored by traditional AV systems
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They can be easily smuggled through emails, documents and archives
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Not subject to close scrutiny by users or administrators
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May be modified by malware on an already infected system
Strategic use of URL files by APT groups
As the analysts point out OPSWAT, even advanced state groups are beginning to use URL files in complex campaigns. They are being used as low-signature tools to initiate attacks – especially when combined with LNK, HTA and PowerShell strings.
Instead of creating new malware from scratch, attackers use a simple URL file as the first step to execute a more complex sequence.
How OPSWAT identifies malicious shortcut files
OPSWAT uses two tools to fully analyze URL files:
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FileTAC – for static inspection (DFI – Deep File Inspection), detects metadata manipulation, hidden values, suspicious fields
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MetaDefender Sandbox – a dynamic environment that analyzes the operation of a URL file in real time, detecting attempts to connect to external servers, create autostart files, download payloads
By combining the two approaches, it is possible to fully identify and neutralize the malicious file – before it has time to do damage.
Summary
URL files are no longer innocent shortcuts to sites – they are becoming a viable threat vector in the cyberattack landscape. Their simplicity makes them attractive to attackers, while users’ inattention and lack of effective analysis tools give them a dangerous window of opportunity. With the help of OPSWAT you can not only detect such files, but also effectively analyze and eliminate them as part of a broader file security strategy. In the next parts of the series, OPSWAT experts will show how to identify threats in URL files at the code and behavioral levels.
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