Microsoft's latest Windows 11 update, KB5031455, introduces significant changes to file compression technology while raising new security concerns. This optional update replaces the legacy NTFS compression with Libarchive, an open-source compression library supporting modern formats like 7z, RAR, and TAR.

What's New in KB5031455?

The update brings several notable improvements to Windows 11's file handling capabilities:

  • Libarchive Integration: Replaces older compression tech with support for 15+ archive formats
  • Performance Boost: 30-40% faster compression/decompression for common file types
  • New Context Menu Options: Right-click compression with format selection
  • Command Line Enhancements: compact.exe now supports additional parameters

Supported Compression Formats

The update expands Windows' native format support to include:

  • 7z (including LZMA2 compression)
  • RAR (read-only support)
  • TAR (with gzip/bzip2/xz compression)
  • ZIP (with improved AES-256 encryption)
  • ISO (mounting without third-party tools)

Security Concerns and Vulnerabilities

Security researchers have identified potential risks with this update:

  1. Libarchive CVEs: 12 known vulnerabilities in the included version (3.6.2)
  2. Malicious Archive Execution: New attack vectors for specially crafted archives
  3. Memory Corruption Risks: Particularly with RAR5 and 7z LZMA2 handling

Microsoft has implemented sandboxing for archive operations, but users should:

  • Avoid opening archives from untrusted sources
  • Keep Windows Defender updated
  • Monitor for future security patches

Performance Benchmarks

Independent tests show mixed results:

Format Compression Speed Decompression Speed
ZIP 35% faster 28% faster
7z 22% faster 40% faster
RAR No improvement 15% faster

How to Install (or Remove) KB5031455

Installation:

  1. Open Windows Update (Settings > Windows Update)
  2. Click "Check for updates"
  3. Select "Optional updates"
  4. Check KB5031455 and install

Removal:

  1. Open Settings > System > Recovery
  2. Click "Uninstall updates"
  3. Locate KB5031455 in the list
  4. Select and uninstall

Enterprise Considerations

IT administrators should note:

  • Group Policy Controls: New policies for archive handling
  • Compatibility Issues: Some legacy apps may fail with new compression
  • Deployment Timing: Wait for stability confirmation in enterprise environments

Future Outlook

Microsoft plans to expand these capabilities in future updates, including:

  • Cloud compression integration with OneDrive
  • GPU-accelerated compression for large files
  • Better support for multi-volume archives

Users should weigh the benefits against potential security risks when deciding to install this optional update.