Hayden

Microsoft’s September 2025 security update revealed a critical vulnerability in the Office suite requiring immediate attention. CVE-2025-54910, classified as a heap-based buffer overflow, allows attackers to execute arbitrary code locally on affected systems.

This vulnerability is particularly concerning because simply opening an Office document—or even previewing it—can compromise system security. This comprehensive guide covers everything from the technical details of the vulnerability to step-by-step remediation procedures.

 

 

1. Understanding CVE-2025-54910: Nature and Risk Assessment

CVE-2025-54910 is a heap-based buffer overflow vulnerability in Microsoft Office that enables attackers to execute local code through maliciously crafted documents. Classified as CWE-122 (Heap-based Buffer Overflow), this vulnerability is especially dangerous because it can be triggered through Office’s preview pane without user interaction.

Key Vulnerability Characteristics

  • Vulnerability Type: Heap-based buffer overflow (CWE-122)
  • Affected Components: Word, Excel, PowerPoint, Visio, and other Office components
  • Attack Vector: Processing of specially crafted Office documents
  • Severity: Critical
  • Disclosure Date: September 9, 2025

The critical nature of this vulnerability stems from its ability to execute attacks through simple document viewing, including file previews in Windows Explorer.

 

 

2. Technical Analysis: Heap Buffer Overflow Mechanics

Heap-based buffer overflows occur when more data is written to a heap-allocated buffer than its allocated capacity. In Office document parsers, this typically manifests through several specific mechanisms.

Root Causes of the Vulnerability

Office document parsers allocate memory on the heap and subsequently write more bytes than the allocated buffer can accommodate. The specific triggers include:

  1. Malformed Embedded Object Fields
    • Incorrect length or size fields in embedded images, OLE streams, and shape metadata
    • Manipulated data causing parsers to allocate smaller buffers than required
  2. Integer Arithmetic Errors
    • Integer overflow/underflow conditions producing smaller-than-intended allocation sizes
    • Arithmetic wraparound leading to incorrect memory calculations
  3. Insufficient Bounds Checking
    • Incomplete validation during decompression, copy, or concatenation operations
    • Missing size verification in data processing routines

Attack Execution Flow

When adjacent heap metadata or object structures are overwritten, attackers can modify pointers or control data structures to redirect execution flow:

  1. Malicious Document Creation: Crafted Office documents designed to trigger heap overflow
  2. Memory Corruption: Document processing overwrites adjacent heap memory regions
  3. Control Flow Hijacking: Manipulation of function pointers or vtable entries
  4. Code Execution: Arbitrary code execution in user context

 

 

3. Affected Products and Version Identification

Impacted Office Products

This vulnerability affects multiple Microsoft Office products and deployment channels:

  • Microsoft 365 Apps for Enterprise
  • Microsoft Office LTSC (Long Term Servicing Channel)
  • Office 2016, 2019, 2021
  • Office Online Server
  • Office for Mac

System Vulnerability Assessment

To check your current Office version:

  1. Through Office Applications
    • Open any Office application (Word, Excel, etc.)
    • Navigate to File → Account → About [Application]
    • Note the product name and version number
  2. Via Control Panel
    • Access Control Panel → Programs and Features
    • Locate Microsoft Office entries and check version information
  3. PowerShell Verification
Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* | Where-Object {$_.DisplayName -like "*Microsoft Office*"} | Select-Object DisplayName, DisplayVersion

 

 

4. Official Microsoft Security Updates and KB Numbers

Microsoft released security updates on September 9, 2025, as part of Patch Tuesday to address this vulnerability. The update includes multiple KB packages for different Office configurations.

Essential KB Update Catalog

Office Product KB Number Update Description
Office Click-to-Run KB5002781 Microsoft 365 Apps security update
Excel 2016 KB5002782 Excel remote code execution fix
Office Online Server KB5002776 Server environment security enhancement
Office 2019 KB5002762 Office 2019 security update
Office LTSC KB5002766 LTSC version security patch

Official Download Sources

Download patches from these official Microsoft channels:

 

 

5. Step-by-Step Patch Implementation Guide

Automatic Update Method (Recommended)

The most reliable approach utilizes Windows Update and Office’s built-in update mechanism.

Step 1: Windows Update Check

  • Navigate to Settings → Update & Security → Windows Update
  • Click Check for updates
  • Install all available updates

Step 2: Office Update Verification

  • Launch any Office application
  • Go to File → Account → Update Options
  • Select Update Now

Manual Patch Download and Installation

For enterprise environments or systems with disabled automatic updates:

Step 1: Current Version Verification

reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\Configuration" /v VersionToReport

Step 2: Appropriate KB Package Download

  • Search Microsoft Update Catalog for relevant KB numbers
  • Select packages matching your system architecture (x86/x64)

Step 3: Patch Installation

  • Execute downloaded .msu files
  • Run installation with administrative privileges
  • Restart system after installation completion

 

 

6. Interim Security Measures and Defense Strategies

For environments unable to immediately apply patches, implement these temporary security controls.

Protected View Enforcement

Mandatory Protected View for internet-sourced and Outlook attachment files provides effective interim protection.

Configuration Steps:

  1. Navigate to File → Options → Trust Center
  2. Select Trust Center Settings → Protected View
  3. Enable all options:
    • Enable Protected View for files originating from the Internet
    • Enable Protected View for files located in potentially unsafe locations
    • Enable Protected View for Outlook attachments

Attack Surface Reduction (ASR) Rules

Configure Microsoft Defender to block Office applications from creating child processes.

PowerShell Implementation:

# Enable ASR rule (audit mode for initial testing)
Add-MpPreference -AttackSurfaceReductionRules_Ids "D4F940AB-401B-4EFC-AADC-AD5F3C50688A" -AttackSurfaceReductionRules_Actions AuditMode

# Convert to block mode after testing
Set-MpPreference -AttackSurfaceReductionRules_Ids "D4F940AB-401B-4EFC-AADC-AD5F3C50688A" -AttackSurfaceReductionRules_Actions Enabled

Additional Security Hardening

  1. Preview Function Disabling
    • Disable Office preview/thumbnail rendering for high-risk mailboxes and servers processing untrusted documents
  2. Application Guard for Office
    • Deploy Application Guard where available to isolate document rendering in containerized environments
  3. Macro Security Enhancement
    • Navigate to File → Options → Trust Center → Macro Settings
    • Select Disable all macros except digitally signed macros

 

 

7. Post-Patch Verification and Validation

Update Success Confirmation

1. Office Version Verification

# Check Office Click-to-Run version
reg query "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office\ClickToRun\Configuration" /v VersionToReport

# Verify installed updates
wmic qfe list full /format:table

2. Event Log Analysis

  • Open Event Viewer → Windows Logs → System
  • Review Microsoft Office-related update installation logs

3. Vulnerability Scanner Utilization

  • Execute full system scan using Windows Security
  • Monitor patch status through WSUS or SCCM in enterprise environments

Post-Patch Functionality Testing

Verify these core functions operate correctly after patch application:

  • Document Handling: Opening/saving various Office document formats
  • Macro Execution: Verifying necessary macro functionality
  • Add-ins/Plugins: Testing third-party Office add-in compatibility
  • Network Integration: Checking SharePoint and OneDrive connectivity

 

 

8. Enterprise-Scale Patch Management Strategy

WSUS/SCCM Centralized Management

Large enterprise environments require systematic deployment approaches:

Phase 1: Test Group Configuration

  • Validate patches in controlled test environments
  • Implement phased rollout to minimize business disruption

Phase 2: Automated Deployment Scripting

# Office update automation script example
$UpdateSession = New-Object -ComObject Microsoft.Update.Session
$UpdateSearcher = $UpdateSession.CreateUpdateSearcher()
$SearchResult = $UpdateSearcher.Search("Type='Software' and IsInstalled=0")

foreach ($Update in $SearchResult.Updates) {
    if ($Update.Title -like "*Office*" -and $Update.Title -like "*KB5002*") {
        Write-Host "Installing: $($Update.Title)"
        # Update installation logic
    }
}

Phase 3: Monitoring and Reporting

  • Real-time patch deployment status monitoring
  • Remediation procedures for failed installations

Compatibility Testing Checklist

Test Category Verification Points Status
Document Compatibility Existing document files open correctly □
Macro Functionality Business-critical macros operate normally □
Plugin Integration Third-party Office plugins function properly □
Network Connectivity SharePoint, Teams integration status □
Print Services Document printing functionality verified □

 

 

Vulnerabilities like CVE-2025-54910 will continue emerging in widely-deployed software like Office due to the complexity of document parsers and the variety of supported file formats. Memory corruption vulnerabilities represent an ongoing threat vector requiring vigilant security practices.

Beyond immediate patch application, establish these long-term security strategies:

  • Regular Security Update Monitoring: Consistent tracking of Microsoft Patch Tuesday releases
  • Layered Defense Implementation: Combining Protected View, ASR rules, and Application Guard
  • User Security Training: Education regarding suspicious attachments and links
  • Backup and Recovery Planning: Comprehensive data protection strategies for incident response

 

 

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