.cab File Extension

What kind of file is a .cab?

A CAB file is a Microsoft Cabinet archive. It bundles one or more files into a binary container and may compress their data. The registered media type is application/vnd.ms-cab-compressed. Microsoft commonly uses cabinets to distribute software, drivers, and installation payloads.¹²

A standard cabinet starts with the ASCII characters MSCF, or the bytes 4D 53 43 46. The header also records the cabinet size, file-table location, and counts of folders and files.² Check the signature when a filename seems suspicious, but remember that four matching bytes alone do not prove that the whole archive is valid or safe.

How do I open a .cab on my computer?

Windows includes tools for Cabinet files. File Explorer can browse many cabinets, while the expand command can list or extract their contents. For example, expand -d package.cab lists members without extracting them. Microsoft also documents expand package.cab -f:* output for extracting all members into an existing destination directory.³

On Windows, macOS, or Linux, use an archive utility that explicitly supports CAB, such as 7-Zip or cabextract. 7-Zip lists CAB as an unpack-only format, so it can extract a cabinet but does not create one.⁴

Poly support for .cab

Poly stores, syncs, shares, versions, and downloads CAB archives. It also makes the archive searchable by filename and ordinary file properties.

Poly does not extract the cabinet, index member names or contents, generate a thumbnail, or provide an in-app archive browser. The Poly agent cannot inspect files that remain packed inside it. To use those files with format-aware Poly features, extract the cabinet locally and add the individual files separately.

History of .cab

Microsoft developed Cabinet for Windows software distribution and installation. The format groups file data into compression units called folders. These are not necessarily source directories. Compression can continue across file boundaries, which can improve compression for related files.²⁵

Cabinets can also form linked sets, a design suited to distribution media with size limits. Windows Installer may reference a separate cabinet or embed one as a stream inside an MSI package.²⁶ CAB predates its registered media type: IANA registered application/vnd.ms-cab-compressed in December 2005.¹

Working with .cab and alternatives

Choose the container for the workflow:

Converting CAB to ZIP means extracting the members and creating a new ZIP archive. Keep the original when it belongs to an installer or linked cabinet set. Repacking does not update an MSI that expects a particular cabinet name, layout, or checksums.