MUM File Format

What is a MUM file?

A MUM file (Microsoft Update Manifest) is an XML-based manifest file used by Windows Update and the Component-Based Servicing (CBS) architecture in Windows Vista and later versions. These files describe the components, dependencies, and installation instructions for Windows updates, features, and system components.

File Extensions

• .mum

MIME Type

• text/xml

History and Development

MUM files were introduced with Windows Vista as part of Microsoft's redesigned update architecture. They replaced the older INF-based system with a more robust, XML-based component management system designed to handle the complexity of modern Windows installations.

Timeline

• 2006: Introduced with Windows Vista and CBS architecture
• 2008: Enhanced with Windows Server 2008
• 2009: Refined with Windows 7
• 2012: Expanded functionality in Windows 8/Server 2012
• Present: Continued evolution with Windows 10/11

Technical Specifications

XML Structure

MUM files are XML documents that follow Microsoft's Component-Based Servicing schema:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v3" 
          manifestVersion="1.0" 
          copyright="Microsoft Corporation">
  
  <assemblyIdentity 
    name="Microsoft-Windows-Example-Component"
    version="10.0.19041.1"
    processorArchitecture="amd64"
    language="neutral"
    buildType="release"
    publicKeyToken="31bf3856ad364e35" />
  
  <package identifier="Package_for_KB1234567" 
           releaseType="Update">
    <parent integrate="derive">
      <assemblyIdentity name="Microsoft-Windows-Foundation-Package"
                       version="10.0.19041.1"
                       processorArchitecture="amd64" />
    </parent>
  </package>
  
</assembly>

Key Elements

• assemblyIdentity: Unique identification of the component
• package: Package information and metadata
• parent: Parent package dependencies
• update: Update-specific information
• customInformation: Additional metadata

Component-Based Servicing (CBS)

Architecture Overview

CBS is Windows' component management system:

• Components: Discrete units of Windows functionality
• Packages: Collections of components for installation
• Features: User-visible functionality units
• Updates: Modifications to existing components

CBS Store Location

C:\Windows\servicing\Packages\

This directory contains:

• MUM files: Component manifests
• CAT files: Digital signature catalogs
• Deployment files: Installation instructions

File Locations and Naming

Standard Locations

# Package manifests
C:\Windows\servicing\Packages\*.mum

# Component manifests  
C:\Windows\WinSxS\Manifests\*.manifest

# CBS logs
C:\Windows\Logs\CBS\CBS.log

Naming Convention

Package_for_KB1234567~31bf3856ad364e35~amd64~~10.0.1.0.mum
|         |            |                |     |    |
|         |            |                |     |    +-- Version
|         |            |                |     +-- Language
|         |            |                +-- Architecture  
|         |            +-- Public Key Token
|         +-- Knowledge Base article
+-- Package identifier

Types of MUM Files

Update Packages

• Security Updates: Critical security patches
• Feature Updates: New functionality additions
• Quality Updates: Bug fixes and improvements
• Cumulative Updates: Combined monthly updates

Component Packages

• Foundation Packages: Core Windows components
• Feature Packages: Optional Windows features
• Language Packages: Localization components
• Driver Packages: Hardware device drivers

Special Packages

• Service Pack Packages: Major update collections
• Hotfix Packages: Targeted fixes for specific issues
• Rollup Packages: Collections of related updates

Manifest Content

Assembly Identity

<assemblyIdentity 
  name="Package_for_KB1234567"
  version="10.0.19041.1"
  processorArchitecture="amd64"
  language="neutral"
  buildType="release"
  publicKeyToken="31bf3856ad364e35"
  versionScope="nonSxS" />

Package Information

<package identifier="KB1234567" 
         releaseType="SecurityUpdate"
         restart="required"
         targetState="Installed">
  
  <updateComponent>
    <assemblyIdentity name="Microsoft-Windows-Kernel32"
                     version="10.0.19041.1"
                     processorArchitecture="amd64" />
  </updateComponent>
  
</package>

Dependencies

<dependency>
  <dependentAssembly>
    <assemblyIdentity name="Microsoft-Windows-Foundation-Package"
                     version="10.0.19041.1"
                     processorArchitecture="amd64" />
  </dependentAssembly>
</dependency>

CBS Tools and Commands

DISM (Deployment Image Servicing and Management)

# List installed packages
dism /online /get-packages

# Get package information
dism /online /get-packageinfo /packagename:Package_for_KB1234567

# Install package
dism /online /add-package /packagepath:C:\path\to\package.mum

# Remove package
dism /online /remove-package /packagename:Package_for_KB1234567

CBS Log Analysis

# View CBS log
type C:\Windows\Logs\CBS\CBS.log | more

# Filter for errors
findstr /i "error" C:\Windows\Logs\CBS\CBS.log

# Search for specific package
findstr "KB1234567" C:\Windows\Logs\CBS\CBS.log

PowerShell Commands

# Get Windows packages
Get-WindowsPackage -Online

# Get specific package
Get-WindowsPackage -Online -PackageName "Package_for_KB1234567"

# Install package
Add-WindowsPackage -Online -PackagePath "C:\path\to\package.mum"

# Remove package
Remove-WindowsPackage -Online -PackageName "Package_for_KB1234567"

Development and Creation

Windows Assessment and Deployment Kit (ADK)

• Package Manager: Create and modify packages
• Component Database: Manage component definitions
• Deployment Tools: DISM and related utilities

Package Creation Process

1. Define Components: Identify files and registry entries
2. Create Manifest: Generate MUM file with metadata
3. Sign Package: Apply digital signatures
4. Test Installation: Verify package functionality
5. Deploy Package: Distribute through update channels

Security and Validation

Digital Signatures

• Catalog Files: .CAT files contain package signatures
• Certificate Validation: Verify Microsoft signatures
• Integrity Checking: Detect tampered packages
• Trust Verification: Ensure package authenticity

Signature Verification

# Verify package signature
signtool verify /v /kp package.cat

# Check catalog integrity
certutil -hashfile package.mum SHA256

Troubleshooting

Common Issues

• Corrupted Manifests: Invalid XML or missing elements
• Dependency Conflicts: Incompatible component versions
• Signature Validation: Failed certificate verification
• Installation Failures: CBS operation errors

Diagnostic Steps

# Run System File Checker
sfc /scannow

# Check CBS log for errors
findstr /i "error\|fail" C:\Windows\Logs\CBS\CBS.log

# Reset CBS store
dism /online /cleanup-image /restorehealth

# Analyze CBS database
dism /online /cleanup-image /analyzecomponentstore

CBS Database Corruption

# Reset Windows Update components
net stop wuauserv
net stop cryptSvc
net stop bits
net stop msiserver

ren C:\Windows\SoftwareDistribution SoftwareDistribution.old
ren C:\Windows\System32\catroot2 catroot2.old

net start wuauserv
net start cryptSvc
net start bits
net start msiserver

Best Practices

System Maintenance

1. Regular Updates: Keep Windows current with latest packages
2. Monitor CBS Logs: Check for installation errors
3. Backup Before Changes: Create system backups before major updates
4. Test Updates: Validate updates in test environments

Administrative Guidelines

• Staged Deployment: Roll out updates gradually
• Compatibility Testing: Verify application compatibility
• Rollback Planning: Prepare for update failures
• Documentation: Maintain update deployment records

Performance Optimization

• Cleanup Operations: Regularly clean CBS store
• Component Store Analysis: Monitor store size and health
• Selective Installation: Only install required components
• Storage Management: Monitor disk space for CBS operations

Enterprise Management

Windows Server Update Services (WSUS)

• Package Distribution: Centralized update deployment
• Approval Process: Control which updates are deployed
• Reporting: Track installation status across organization
• Group Policies: Configure automatic update behavior

System Center Configuration Manager

• Software Updates: Advanced update management
• Compliance Monitoring: Track update installation status
• Maintenance Windows: Schedule update installations
• Rollback Capability: Uninstall problematic updates

MUM files are fundamental to Windows' modern update architecture, providing the metadata and instructions necessary for reliable, secure component management. Understanding their structure and role is essential for Windows system administration and troubleshooting.