CVE-2025-21356
📋 TL;DR
This vulnerability allows remote code execution when a user opens a specially crafted Visio file. Attackers could exploit this to run arbitrary code with the privileges of the current user. All users running affected versions of Microsoft Visio are potentially vulnerable.
💻 Affected Systems
- Microsoft Office Visio
📦 What is this software?
365 Apps by Microsoft
365 Apps by Microsoft
Office by Microsoft
Office by Microsoft
Office Long Term Servicing Channel by Microsoft
View all CVEs affecting Office Long Term Servicing Channel →
Office Long Term Servicing Channel by Microsoft
View all CVEs affecting Office Long Term Servicing Channel →
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining same privileges as the user, potentially leading to data theft, ransomware deployment, or lateral movement within the network.
Likely Case
Malicious actor tricks user into opening a crafted Visio file, leading to malware installation, credential theft, or system disruption.
If Mitigated
Limited impact due to user awareness training, application whitelisting, and proper email/web filtering blocking malicious files.
🎯 Exploit Status
Requires user interaction (opening malicious file). Exploit likely involves heap-based buffer overflow (CWE-122) manipulation in Visio file parsing.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft's monthly security updates for Visio; specific version would be in the advisory.
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21356
Restart Required: No
Instructions:
1. Open Visio. 2. Go to File > Account > Update Options > Update Now. 3. Alternatively, use Microsoft Update or Windows Update to install the latest security updates for Office/Visio.
🔧 Temporary Workarounds
Block Visio file attachments
allConfigure email gateways and web filters to block .vsd, .vsdx, and other Visio file extensions from untrusted sources.
Open in Protected View
windowsConfigure Visio to open files from the internet in Protected View by default to prevent automatic code execution.
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized executables from running.
- Educate users to never open Visio files from untrusted sources and to verify sender authenticity.
🔍 How to Verify
Check if Vulnerable:
Check Visio version via File > Account > About Visio and compare with Microsoft's advisory for affected versions.Check Version:
In Visio: File > Account > About Visio (no command line option available)Verify Fix Applied:
Verify that the latest security updates from Microsoft are installed and that the Visio version matches the patched version in the advisory.📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing Visio crashes, unexpected process creation from Visio.exe, or suspicious file opens
Network Indicators:
- Unusual outbound connections from systems running Visio, especially to known malicious IPs
SIEM Query:
Process Creation where Image contains 'visio.exe' AND ParentImage contains 'explorer.exe' AND CommandLine contains suspicious file extensions