CVE-2025-26630: Microsoft 365 Apps Use-After-Free Flaw

CVE-2025-26630 Overview

CVE-2025-26630 is a use-after-free vulnerability affecting Microsoft Office Access that allows an unauthorized attacker to execute arbitrary code locally. This memory corruption flaw occurs when the application incorrectly handles memory after it has been freed, enabling attackers to manipulate freed memory regions and potentially gain control over program execution flow.

Critical Impact

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code with the privileges of the current user, potentially leading to complete system compromise if the user has administrative rights.

Affected Products

• Microsoft 365 Apps for Enterprise
• Microsoft Access 2016
• Microsoft Office 2019
• Microsoft Office Long Term Servicing Channel 2021
• Microsoft Office Long Term Servicing Channel 2024

Discovery Timeline

• 2025-03-11 - CVE-2025-26630 published to NVD
• 2025-07-03 - Last updated in NVD database

Technical Details for CVE-2025-26630

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free), a memory corruption vulnerability class that occurs when an application continues to use a pointer after the memory it references has been deallocated. In the context of Microsoft Office Access, this flaw allows attackers to craft malicious files that trigger the use-after-free condition when processed by the application.

The local attack vector requires user interaction, meaning a victim must open a specially crafted Access database file or document for the vulnerability to be triggered. Once exploited, the attacker could achieve code execution within the context of the user's session, potentially compromising confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause of CVE-2025-26630 lies in improper memory management within Microsoft Office Access. Specifically, the application fails to properly validate or clear references to memory objects after they have been freed. This creates a dangling pointer scenario where subsequent operations may reference the freed memory location, which could now contain attacker-controlled data.

Use-after-free vulnerabilities typically arise from:

• Inadequate reference counting for dynamically allocated objects
• Missing null pointer assignments after memory deallocation
• Race conditions between memory free operations and object usage
• Complex object lifecycle management in multi-threaded environments

Attack Vector

The attack requires local access and user interaction to succeed. An attacker would need to convince a user to open a maliciously crafted Microsoft Access file (such as .accdb or .mdb files). The attack scenario typically involves:

1. Delivery: The attacker delivers a specially crafted Access database file via email attachment, web download, or shared network location
2. User Interaction: The victim opens the malicious file in Microsoft Access
3. Trigger: The malformed file triggers the use-after-free condition during parsing or processing
4. Exploitation: The freed memory is reallocated with attacker-controlled content, allowing hijacking of program execution

The vulnerability mechanism involves memory corruption that can be exploited to gain control of program flow. The malicious Access file would contain specifically crafted data structures designed to trigger premature memory deallocation while maintaining references to the freed memory region. For detailed technical information, refer to the Microsoft Security Update Guide.

Detection Methods for CVE-2025-26630

Indicators of Compromise

• Unusual Microsoft Access (MSACCESS.EXE) process behavior, including unexpected child processes or network connections
• Crash dumps or Windows Error Reporting events associated with Microsoft Access indicating memory access violations
• Suspicious Access database files with anomalous file structures or unexpected embedded content
• Evidence of code execution originating from Access process memory space

Detection Strategies

• Deploy endpoint detection rules to monitor for abnormal memory operations within Microsoft Access processes
• Implement file inspection capabilities to identify potentially malicious Access database files before user interaction
• Configure application crash monitoring to detect exploitation attempts that result in process termination
• Utilize behavioral analysis to identify post-exploitation activities following Access file opening

Monitoring Recommendations

• Enable enhanced logging for Microsoft Office applications to capture file access and process behavior
• Monitor for suspicious parent-child process relationships where MSACCESS.EXE spawns unexpected executables
• Implement network segmentation monitoring to detect potential lateral movement following exploitation
• Configure SIEM alerting for clusters of Access-related crashes that may indicate active exploitation attempts

How to Mitigate CVE-2025-26630

Immediate Actions Required

• Apply the latest Microsoft security updates for affected Office products immediately
• Restrict user permissions to prevent opening untrusted Access database files from external sources
• Enable Protected View in Microsoft Office to provide a sandboxed environment for opening files from untrusted locations
• Educate users about the risks of opening Access files from unknown or untrusted sources

Patch Information

Microsoft has released security updates to address CVE-2025-26630. Organizations should apply patches for all affected products including Microsoft 365 Apps for Enterprise, Microsoft Access 2016, Microsoft Office 2019, and Microsoft Office LTSC 2021/2024. Detailed patch information is available in the Microsoft Security Update Guide for CVE-2025-26630.

Workarounds

• Block or quarantine Access database files (.accdb, .mdb, .accde, .accdr) at email gateways and web proxies until patches can be applied
• Configure Microsoft Office Trust Center settings to block files originating from the Internet zone
• Implement application control policies to restrict Access database execution to approved locations only
• Consider temporarily disabling Microsoft Access for non-essential users until patching is complete

# PowerShell: Check installed Office version for patch verification
Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* | 
Where-Object { $_.DisplayName -like "*Microsoft Office*" -or $_.DisplayName -like "*Microsoft 365*" } | 
Select-Object DisplayName, DisplayVersion, InstallDate