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.msu (Microsoft Update) file format

.msu  ·  package (CAB wrapper)  ·  introduced 2007 by Microsoft

What is a .msu (Microsoft Update) file?

.msu files are Microsoft Update Standalone Installer packages — a CAB archive containing one or more inner CABs, an XML manifest, and metadata. Windows Update downloads many cumulative updates as MSUs, and 7-Zip can browse straight into them.

Most readers reach this page after double-clicking a .msu file and finding their operating system unsure what to do with it. The good news: .msu (Microsoft Update) is a well-understood format with mature tooling on every major platform. It is supported in one click by mainstream archivers on Windows, macOS, and Linux.

How to extract a .msu (Microsoft Update) file

Opening a .msu file is straightforward on every modern operating system. The exact steps depend on which platform you are on:

On Windows

1. Locate the .msu file in File Explorer.
2. Right-click the file. If you have 7-Zip installed, choose 7-Zip → Extract Here. On Windows 11 the built-in extractor handles ZIP, 7z, RAR and several other formats directly through Extract All…
3. If prompted, pick a destination folder and click Extract.
4. The extracted files appear in a folder next to the original archive.

On macOS

1. Find the .msu file in Finder.
2. Install The Unarchiver from the Mac App Store, or Keka for both creating and extracting.
3. Right-click the file → Open With → The Unarchiver (or just double-click after Unarchiver is set as the default).
4. The extracted folder appears next to the archive.

On Linux

1. Use your file manager: right-click the archive → Extract Here (file-roller on GNOME, Ark on KDE).
2. On the command line, run one of:

   7z x archive.msu    # works for almost any format

3. The files appear in the current directory.

How to create a .msu (Microsoft Update) file

To pack files into a .msu archive, you typically need an archiver that supports writing this format. Not every tool can create every format — for example, only WinRAR can create real RAR files. The sidebar lists the software known to read and write .msu (Microsoft Update).

On the command line, the canonical create command is:

# Use 7-Zip, PeaZip, or the format's reference tool to create .msu files.

If you regularly create archives at scale, a dedicated archive automation suite can wrap this command in scheduled jobs, integrity checks, and offsite replication.

Strengths

• Self-contained update unit
• Inspectable with 7-Zip

Weaknesses and limitations

• Layered nested CABs
• Windows-specific

Typical use cases

• Windows offline updates
• Enterprise patching

Technical details

.msu (Microsoft Update) uses the CAB inside CAB algorithm and is identified on disk by the magic byte sequence 4D 53 43 46. The standard MIME type is application/x-msu. The format is a proprietary specification and is free for any use.

Frequently asked questions

Is .msu (Microsoft Update) safe to open?

Archive files are containers — they are only as safe as what they contain. A .msu from a trusted source is fine; one received from a stranger can hold malicious executables, scripts, or files engineered to exploit bugs in your archiver. Always keep your archiver updated, and never run unknown executables that come out of an archive. A safe workflow is to extract into a sandbox and scan the contents before opening anything.

What is the maximum file size?

Modern implementations support archives in the multi-terabyte range. The practical limit is your filesystem (FAT32 caps at 4 GB; ext4, NTFS, APFS, and exFAT all comfortably handle multi-TB files).

Can I password-protect a .msu (Microsoft Update)?

Some archivers can wrap .msu (Microsoft Update) files in an encrypted container, but the format itself does not always include built-in encryption. Check your archiver's documentation.

How does .msu (Microsoft Update) compare to other formats?

See our format comparison pages such as ZIP vs 7z, ZIP vs RAR, and tar.gz vs tar.xz for side-by-side feature tables.

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