Researching file formats 17: Shell link binary file format

Shell Link Binary File Format
Formal name: Shell Link Binary File Format
Informal name / also known as / previously known as: Microsoft Windows Shortcut

Link files are a little bit sneaky. They appear on the Windows graphical user interface (the Desktop, folders, et al) without a file extension and with an illustration of an arrow in the bottom left corner, but no visible file extension – Windows hides that. Also any folder that is “My Recent Documents” or whatever will be composed of these link files, too.

For a long while, this file was opaque and had to be reverse engineered for any analysis. Microsoft has since fully put the specification and history online, at least since 2010. (But the file has been around for a good many years before that… like 15 years.) Prior versions are acknowledged in the version history on the website and in the specification draft but not available.

This format let me explore the malware potential of files for a little bit, as LNK files have been used to make computers go boom-boom-boom, like this malware case. I can really appreciate the infosec community when they do so much open reporting on vulnerabilities, and in general the formal practice of private disclosure and, if necessary or at the appropriate time, public disclosure.

I like how malware always have cute names. One of the ones impacting this format is called “Raspberry Robin”. It’s a worm!