What is the CAB file format?
.cab is an installer archive developed by Microsoft. Windows uses many automated software installation tools that utilize .cab archives. .cab files store system files, libraries, device drivers, network protocols, configuration files, and other resources needed by a given application to be installed.
Every .cab file begins with the four-byte ASCII signature MSCF (hex 4D 53 43 46) at byte offset 0, followed by a structured cabinet header. Its registered MIME type is application/vnd.ms-cab-compressed.
CAB file compression
Data in .cab archives is compressed using one of the following algorithms:
- MSZIP (a deflate-compatible method, similar to a ZIP archive),
- Quantum,
- LZX.
Digital signature
Besides various compression methods, the .cab format also supports digital signatures. Digital signatures can be used to verify the authenticity of software packages stored in .cab files.
Other installer formats that use CAB
.cab archives are a core component of Windows Installer - .cab payloads are embedded in or referenced by .MSI packages and .MSU update bundles. On Windows, .cab files can be extracted with the built-in expand.exe command or browsed directly in File Explorer. Third-party tools may also consume .cab files, though compatibility with Windows-supplied packages is not guaranteed.
Security & safety
RISK: MEDIUMA .cab is an archive, so its risk is the risk of its contents - driver/update cabs are safe from Microsoft and Windows Update, but a .cab from an unknown source can carry malicious executables or fake driver installers. Prefer signed cabinets; cabs delivered by Windows Update or vendor sites are verified, those attached to e-mails are not. Extract and inspect before running anything inside.
Format details
in a nutshellPrograms that open CAB files
Windows5 apps
File Explorer (built-in)
Built-in Double-click the .cab to browse it; drag files out, or right-click a file → Extract.
expand.exe / DISM (built-in)
Built-in Run: expand driver.cab -F:* C:\out (or DISM /Add-Driver for driver cabs). 
macOS1 app
Linux2 apps
Xarchiver / GNOME Archive Manager
Open-source Open the .cab in the GUI archive manager (uses cabextract under the hood). Technical details
deep spec| File signature (magic bytes) | `MSCF` - hex `4D 53 43 46` at byte offset 0 |
| MIME type | `application/vnd.ms-cab-compressed` |
| Format type | Binary compressed archive container |
| Compression algorithms | MSZIP (deflate-compatible), Quantum, LZX - one algorithm per cabinet folder |
| Internal structure | Cabinet header → folder descriptors → file entries → compressed data blocks |
| Multi-cabinet spanning | Large archives can be split across multiple `.cab` files, linked via next/previous cabinet name fields in the header |
| Maximum files per cabinet | Up to 65,535 files in a single cabinet |
| Folder-level compression | Each folder within a cabinet is compressed independently, allowing mixed compression algorithms in one archive |
| Digital signature support | Supports Authenticode code-signing for verifying the authenticity of packaged content |
| Per-file metadata | Stores filename, uncompressed size, last-modified date and time, and DOS file attributes |
| Cabinet checksum | Optional 32-bit checksum fields at cabinet and data-block level for integrity verification |
| Windows built-in tools | `expand.exe` (command-line extraction), File Explorer (GUI browse), `dism.exe` for Windows Update `.cab` packages |
| Developer | Microsoft Corporation |
| Deployment integration | Payloads are embedded in or referenced by `.msi` Windows Installer packages, `.msu` update bundles, and `.exe` self-extractors |
| Released | 1990s (Microsoft Cabinet, MS-CAB); used since early Windows setup |
| Open standard | Yes · royalty-free |
| Specification | learn.microsoft.com |
CAB conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about CAB files.
