CVE-2025-21356: Microsoft Office Visio RCE Vulnerability

CVE-2025-21356 Overview

CVE-2025-21356 is a Remote Code Execution vulnerability affecting Microsoft Office Visio. This vulnerability allows attackers to execute arbitrary code on affected systems through specially crafted Visio files. The attack requires user interaction, specifically opening a malicious file, but once triggered can result in complete system compromise with the privileges of the current user.

Critical Impact
Successful exploitation allows attackers to execute arbitrary code with user privileges, potentially leading to full system compromise, data theft, and lateral movement within enterprise networks.

Affected Products

Microsoft 365 Apps for Enterprise (x64 and x86)
Microsoft Office 2019 (x64 and x86)
Microsoft Office Long Term Servicing Channel 2021 (x64 and x86)
Microsoft Office Long Term Servicing Channel 2024 (x64 and x86)

Discovery Timeline

2025-01-14 - CVE-2025-21356 published to NVD
2025-07-01 - Last updated in NVD database

Technical Details for CVE-2025-21356

Vulnerability Analysis

This vulnerability is classified under CWE-122 (Heap-based Buffer Overflow), indicating a memory corruption issue in Microsoft Office Visio's file parsing functionality. The heap-based buffer overflow occurs when Visio processes maliciously crafted diagram files, allowing attackers to corrupt memory structures and potentially redirect program execution flow.

The local attack vector means an attacker must deliver a malicious file to the target user, typically through phishing emails, compromised websites, or file-sharing services. While user interaction is required to open the file, no additional authentication or elevated privileges are needed to trigger the vulnerability.

Root Cause

The vulnerability stems from improper bounds checking during the parsing of Visio diagram files. When processing certain file structures, the application fails to properly validate input sizes before copying data to heap-allocated buffers. This allows attackers to overflow the buffer boundaries, corrupting adjacent memory structures and potentially gaining control of program execution.

Attack Vector

The attack leverages the local attack vector with a requirement for user interaction. An attacker would craft a malicious Visio file (.vsd, .vsdx, or related formats) containing specially structured data designed to trigger the heap buffer overflow. The attack sequence typically involves:

Attacker creates a weaponized Visio file with malformed structures
File is delivered to target via email attachment, file share, or web download
Victim opens the file in Microsoft Visio
Visio parses the malformed content, triggering the heap overflow
Attacker's payload executes with the victim's user privileges

The vulnerability does not require any special conditions beyond user interaction, making it relatively straightforward to exploit once a malicious file reaches the target.

Detection Methods for CVE-2025-21356

Indicators of Compromise

Unusual Visio file activity, particularly files received from external or unknown sources
Unexpected child processes spawned by VISIO.EXE
Anomalous memory access patterns or crash dumps from the Visio application
Suspicious network connections originating from Visio processes

Detection Strategies

Monitor for Visio processes (VISIO.EXE) spawning unexpected child processes such as cmd.exe, powershell.exe, or scripting interpreters
Implement file integrity monitoring to detect modifications to Visio executables and DLLs
Deploy endpoint detection rules for heap spray patterns and shellcode execution signatures
Enable Windows Defender Application Guard for Office documents from untrusted sources

Monitoring Recommendations

Configure SIEM alerts for anomalous Visio file access patterns across the organization
Enable Microsoft Defender for Endpoint detections specific to Office application exploitation
Monitor for suspicious Visio files with unusual embedded objects or OLE components
Track email attachments containing Visio file formats from external senders

How to Mitigate CVE-2025-21356

Immediate Actions Required

Apply Microsoft security updates immediately through Windows Update or WSUS
Enable Protected View for files downloaded from the internet
Restrict Visio file access from untrusted sources pending patch deployment
Educate users about the risks of opening Visio files from unknown sources

Patch Information

Microsoft has released security updates to address this vulnerability. Organizations should apply patches through their standard update channels. Detailed patch information and affected version numbers are available in the Microsoft Security Response Center advisory.

For enterprise environments, deploy updates via:

Microsoft Endpoint Configuration Manager
Windows Server Update Services (WSUS)
Microsoft 365 Apps admin center
Manual download from Microsoft Update Catalog

Workarounds

Enable Protected View for all Office documents by default
Configure Microsoft Defender Application Guard for Office to isolate document processing
Implement email gateway filtering to quarantine Visio attachments from external sources
Deploy Attack Surface Reduction (ASR) rules to block Office applications from creating child processes

bash

# PowerShell: Enable ASR rule to block Office apps from creating child processes
Add-MpPreference -AttackSurfaceReductionRules_Ids D4F940AB-401B-4EFC-AADC-AD5F3C50688A -AttackSurfaceReductionRules_Actions Enabled

# Verify ASR rule is enabled
Get-MpPreference | Select-Object -ExpandProperty AttackSurfaceReductionRules_Ids