CVE-2025-27745: Microsoft 365 Apps Use After Free Flaw

CVE-2025-27745 Overview

CVE-2025-27745 is a use-after-free vulnerability in Microsoft Office that allows an unauthorized attacker to execute arbitrary code locally. This memory corruption flaw occurs when the application continues to reference memory after it has been freed, potentially allowing attackers to manipulate program execution flow and achieve code execution on the target system.

Critical Impact

Successful exploitation of this use-after-free vulnerability could allow attackers to execute arbitrary code with the privileges of the current user, potentially leading to full system compromise when targeting privileged accounts.

Affected Products

• Microsoft 365 Apps for Enterprise
• Microsoft Office 2016, 2019
• Microsoft Office Long Term Servicing Channel 2021 (Windows and macOS)
• Microsoft Office Long Term Servicing Channel 2024 (Windows and macOS)

Discovery Timeline

• April 8, 2025 - CVE-2025-27745 published to NVD
• July 9, 2025 - Last updated in NVD database

Technical Details for CVE-2025-27745

Vulnerability Analysis

This vulnerability is classified as CWE-416: Use After Free, a memory corruption class that occurs when a program continues to use a pointer after the memory it references has been freed. In the context of Microsoft Office, this flaw can be triggered when processing specially crafted documents that manipulate memory allocation patterns within the application.

The attack requires local access and user interaction, meaning a victim must open a malicious Office document for exploitation to occur. Upon successful exploitation, the attacker gains the ability to execute arbitrary code within the context of the Office application, inheriting all permissions of the current user.

Use-after-free vulnerabilities in complex applications like Microsoft Office are particularly dangerous because the application manages numerous object types and memory allocations during document processing, providing multiple potential exploitation primitives.

Root Cause

The root cause of CVE-2025-27745 lies in improper memory management within Microsoft Office. The vulnerability manifests when the application fails to properly invalidate references to freed memory objects. When memory is deallocated but pointers to that memory remain accessible, subsequent operations may inadvertently reuse the freed memory location, leading to undefined behavior that attackers can exploit for code execution.

Attack Vector

Exploitation of this vulnerability requires local access to the target system and user interaction. The typical attack scenario involves:

1. An attacker crafts a malicious Office document (such as .docx, .xlsx, or .pptx) containing content designed to trigger the use-after-free condition
2. The attacker delivers the malicious document to the victim through various means such as email attachments, file shares, or download links
3. When the victim opens the document with a vulnerable version of Microsoft Office, the application processes the malicious content
4. The use-after-free condition is triggered, allowing the attacker to manipulate memory and achieve code execution

The attacker must convince the user to open the malicious file, making social engineering an important component of real-world exploitation attempts.

Detection Methods for CVE-2025-27745

Indicators of Compromise

• Unexpected Microsoft Office application crashes when opening documents from untrusted sources
• Office processes spawning unusual child processes (e.g., cmd.exe, powershell.exe, or mshta.exe)
• Anomalous memory allocation patterns in Office application event logs
• Documents from external sources triggering Windows Defender or endpoint protection alerts

Detection Strategies

• Enable and monitor Application Crash Reports for Microsoft Office applications to identify potential exploitation attempts
• Deploy endpoint detection and response (EDR) solutions to monitor Office processes for suspicious behavior patterns
• Implement email gateway scanning to detect and quarantine potentially malicious Office documents before delivery
• Configure behavioral detection rules for Office applications spawning suspicious child processes

Monitoring Recommendations

• Monitor Windows Event Logs for application crashes involving WINWORD.EXE, EXCEL.EXE, POWERPNT.EXE, and other Office binaries
• Track network connections initiated by Office applications to identify potential command-and-control communications
• Implement file integrity monitoring for Office application directories to detect unauthorized modifications
• Review security audit logs for unusual document access patterns that may indicate reconnaissance or exploitation attempts

How to Mitigate CVE-2025-27745

Immediate Actions Required

• Apply the latest Microsoft security updates for all affected Office products immediately
• Enable Protected View and Application Guard for Office to isolate potentially malicious documents
• Educate users about the risks of opening Office documents from untrusted or unknown sources
• Consider blocking Office file types at the email gateway from external senders until patching is complete

Patch Information

Microsoft has released security updates to address CVE-2025-27745. Detailed patch information and download links are available in the Microsoft Security Update Guide. Organizations should prioritize patching based on their deployment of affected products:

• Microsoft 365 Apps for Enterprise: Update through Microsoft 365 Admin Center or Windows Update
• Microsoft Office 2016/2019: Apply the latest cumulative updates via Windows Update or WSUS
• Office LTSC 2021/2024: Deploy updates through standard enterprise patch management processes

Workarounds

• Enable Protected View for all Office documents originating from the Internet, email attachments, or potentially unsafe locations
• Configure Office Application Guard (available in Microsoft 365 Apps for Enterprise) to open documents in isolated containers
• Implement application whitelisting to restrict Office applications from executing unexpected child processes
• Use Group Policy to enable Block macros from running in Office files from the Internet setting

# PowerShell: Verify Office Protected View settings are enabled
Get-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Word\Security\ProtectedView" -Name "DisableInternetFilesInPV" -ErrorAction SilentlyContinue
Get-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" -Name "DisableInternetFilesInPV" -ErrorAction SilentlyContinue

# Value of 0 means Protected View is enabled (default and secure)
# Value of 1 means Protected View is disabled (insecure)