CVE-2021-27055
📋 TL;DR
CVE-2021-27055 is a security feature bypass vulnerability in Microsoft Visio that allows attackers to circumvent security controls when opening specially crafted files. This affects users who open untrusted Visio files, potentially leading to unauthorized actions. The vulnerability requires user interaction through opening a malicious file.
💻 Affected Systems
- Microsoft Visio
📦 What is this software?
365 Apps by Microsoft
Office by Microsoft
Visio by Microsoft
Visio by Microsoft
Visio by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
An attacker could bypass security features to execute arbitrary code with the privileges of the current user, potentially leading to full system compromise if combined with other vulnerabilities.
Likely Case
Attackers bypass security warnings to trick users into opening malicious files, leading to limited system access or data theft.
If Mitigated
With proper controls, the impact is limited to the user's session and isolated through application sandboxing.
🎯 Exploit Status
Requires social engineering to deliver malicious file; user must open the file.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Security updates released in March 2021
Vendor Advisory: https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-27055
Restart Required: Yes
Instructions:
1. Open Microsoft Visio. 2. Go to File > Account > Update Options > Update Now. 3. Install available updates. 4. Restart Visio when prompted.
🔧 Temporary Workarounds
Block .vsdx files via email filtering
allConfigure email gateways to block or quarantine .vsdx attachments from untrusted sources.
Disable Visio file preview
windowsDisable preview of Visio files in Windows Explorer to prevent automatic parsing.
reg add "HKCU\Software\Classes\.vsdx" /v "PerceivedType" /t REG_SZ /d "" /f
🧯 If You Can't Patch
- Restrict Visio usage to trusted users only and implement application whitelisting.
- Educate users about the risks of opening untrusted Visio files and implement strict file validation procedures.
🔍 How to Verify
Check if Vulnerable:
Check Visio version via File > Account > About Visio. If version is prior to March 2021 updates, it's vulnerable.Check Version:
In Visio: File > Account > About VisioVerify Fix Applied:
Verify Visio version is updated to March 2021 or later security updates.📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs showing Visio crashes or suspicious file opens
- Antivirus alerts for malicious .vsdx files
Network Indicators:
- Unusual outbound connections after opening Visio files
- File downloads of .vsdx from untrusted sources
SIEM Query:
source="Windows Security" EventID=4688 ProcessName="VISIO.EXE" | stats count by host