.CAB file signature
A Microsoft Cabinet archive data file begins with the bytes 4D 53 43 46 (MSCF in ASCII) at the start of the file. The signature is the same whatever the file is named, which is why a renamed or extensionless CAB file is still recognisable.
Signature
| Offset | Hex | ASCII |
|---|---|---|
| 0 | 4D 53 43 46 | MSCF |
MIME type: application/vnd.ms-cab-compressed · usual extensions: .cab
How to check a file's signature
Without installing anything: drop the file on our detector. It reads the bytes in your browser and shows the hex dump alongside the verdict; nothing is uploaded.
macOS and Linux (Terminal):
xxd -l 32 file.cab
file file.cabWindows (PowerShell):
Format-Hex -Path file.cab -Count 32If the bytes do not match
A file named .cab whose first bytes are something else is not a CAB file. The common explanations are a wrong or deliberately misleading extension, a download that saved an HTML error page instead of the file, or a container such as ZIP wrapping the real content. The detector reports what the bytes say; the CAB guide explains what a genuine file should contain.