Cabinet (CAB) file signature
Magic number at the start of the file · MSCF
Microsoft Cabinet archives start with the ASCII magic MSCF, then a reserved zero field and the total cabinet size. CAB is used inside Windows installers and driver packages.
What this magic number means
A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 4D 53 43 46 (the text MSCF), it is a Cabinet (CAB) file.
Formats that use the 4D 53 43 46 signature
These file types in our database carry this signature:
How to check a file's signature
You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.cab
- hexdump -C -n 16 example.cab
- file example.cab
Windows (PowerShell)
- Format-Hex -Path example.cab -Count 16
Python
- open("example.cab","rb").read(4).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the Cabinet (CAB) file signature?
Cabinet (CAB) files start with the hex bytes 4D 53 43 46 (MSCF in ASCII). This magic number identifies the format regardless of the file's name or extension.
How do I check a file's magic number?
Open the file in a hex editor, or run a command such as xxd -l 16 example.cab on Linux or macOS, or Format-Hex -Path example.cab -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the Cabinet (CAB) signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine Cabinet (CAB) file has these exact bytes; a file with the wrong bytes is not really Cabinet (CAB), whatever its name says.