CVE-2025-27750: Microsoft 365 Apps Use-After-Free Flaw

CVE-2025-27750 Overview

CVE-2025-27750 is a use-after-free vulnerability affecting Microsoft Office Excel that allows an unauthorized attacker to execute arbitrary code locally. This memory corruption flaw occurs when Excel improperly handles memory during file processing operations, potentially allowing attackers to manipulate freed memory regions to gain code execution within the context of the current user.

Critical Impact

Successful exploitation of this use-after-free vulnerability enables attackers to execute arbitrary code with the privileges of the logged-in user, potentially leading to complete system compromise, data theft, or further lateral movement within an organization.

Affected Products

• Microsoft 365 Apps for Enterprise
• Microsoft Excel 2016
• Microsoft Office 2019
• Microsoft Office LTSC 2021 (Windows and macOS)
• Microsoft Office LTSC 2024 (Windows and macOS)

Discovery Timeline

• April 8, 2025 - CVE-2025-27750 published to NVD
• July 9, 2025 - Last updated in NVD database

Technical Details for CVE-2025-27750

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability that occurs when a program continues to use a pointer after the memory it references has been deallocated. In the context of Microsoft Excel, this condition can be triggered when processing specially crafted spreadsheet files.

The attack requires local access and user interaction, meaning an attacker must convince a victim to open a malicious Excel file. Once the user opens the crafted document, the use-after-free condition is triggered, allowing the attacker to potentially control the contents of the freed memory region and redirect program execution to attacker-controlled code.

The vulnerability affects core Excel functionality across multiple Microsoft Office product lines, including both subscription-based Microsoft 365 Apps and perpetually licensed Office LTSC versions for both Windows and macOS platforms.

Root Cause

The root cause of CVE-2025-27750 lies in improper memory management within Microsoft Excel's file parsing routines. When processing certain Excel file structures, the application deallocates memory but maintains a stale reference (dangling pointer) to the freed memory region. Subsequent operations that reference this pointer can lead to memory corruption when the freed memory is reallocated for other purposes, creating an exploitable condition.

Attack Vector

The attack vector for this vulnerability is local, requiring the attacker to deliver a malicious Excel file to the victim through various means such as email attachments, file-sharing services, or compromised network shares. The attack requires user interaction—specifically, the victim must open the malicious file in a vulnerable version of Microsoft Excel.

Upon opening the crafted file, the use-after-free condition is triggered during document parsing. An attacker who successfully exploits this vulnerability could achieve arbitrary code execution with the same privileges as the current user. If the user has administrative privileges, the attacker could gain full control of the affected system.

The vulnerability mechanism involves memory corruption during Excel file processing. When Excel processes specific document structures in a malicious file, it frees a memory object but retains a pointer reference. Subsequent operations using this dangling pointer allow an attacker to potentially control memory contents and hijack program execution flow. For complete technical details, refer to the Microsoft Security Update Guide.

Detection Methods for CVE-2025-27750

Indicators of Compromise

• Unexpected Excel process crashes or abnormal behavior when opening spreadsheet files from untrusted sources
• Excel processes spawning child processes or making unusual network connections
• Memory access violations logged in Windows Event Logs associated with EXCEL.EXE
• Suspicious Excel files with anomalous internal structures or embedded objects

Detection Strategies

• Deploy endpoint detection rules to monitor for abnormal Excel process behavior, including unexpected child process creation
• Implement file inspection capabilities to scan incoming Excel attachments for malformed or suspicious content
• Enable Protected View and Application Guard for Office documents from untrusted sources
• Monitor for heap corruption indicators and access violation events in Excel processes

Monitoring Recommendations

• Configure SentinelOne to detect and block exploitation attempts targeting Office applications
• Enable enhanced logging for Office application events and memory protection violations
• Monitor email gateways for suspicious Excel file attachments with anomalous structures
• Implement behavioral analysis to detect post-exploitation activities following document opening

How to Mitigate CVE-2025-27750

Immediate Actions Required

• Apply the latest Microsoft security updates for all affected Office products immediately
• Enable Protected View for documents originating from the internet, email, or untrusted locations
• Configure Microsoft Defender Application Guard for Office to isolate untrusted documents
• Educate users about the risks of opening Excel files from unknown or untrusted sources

Patch Information

Microsoft has released security updates to address this vulnerability. Organizations should apply patches through Windows Update, Microsoft Update Catalog, or enterprise patch management solutions such as WSUS or Microsoft Endpoint Configuration Manager.

For detailed patch information and download links, consult the Microsoft Security Update Guide for CVE-2025-27750.

Workarounds

• Enable Protected View for all Office documents to prevent automatic execution of potentially malicious content
• Use Microsoft Defender Application Guard for Office to open untrusted documents in an isolated container
• Block Excel file attachments at the email gateway from untrusted external sources
• Restrict macro execution using Group Policy to reduce additional attack surface

# Registry configuration to enforce Protected View for internet files
reg add "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" /v DisableInternetFilesInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" /v DisableAttachementsInPV /t REG_DWORD /d 0 /f
reg add "HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView" /v DisableUnsafeLocationsInPV /t REG_DWORD /d 0 /f