CVE-2025-21383
📋 TL;DR
This vulnerability in Microsoft Excel allows an attacker to read sensitive information from memory when a specially crafted file is opened. It affects users who open untrusted Excel files, potentially exposing confidential data like passwords or system information. The vulnerability requires user interaction through file opening.
💻 Affected Systems
- Microsoft Excel
📦 What is this software?
365 Apps by Microsoft
365 Apps by Microsoft
Excel by Microsoft
Excel 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 →
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
Complete memory disclosure leading to credential theft, sensitive document exposure, or system compromise if combined with other vulnerabilities.
Likely Case
Limited information disclosure from Excel's memory space, potentially exposing fragments of other documents or system data.
If Mitigated
No impact if users don't open untrusted files or if proper application sandboxing is in place.
🎯 Exploit Status
Requires social engineering to get user to open malicious file. No known active exploitation at disclosure.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: As specified in Microsoft's monthly security updates
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21383
Restart Required: Yes
Instructions:
1. Open Excel. 2. Go to File > Account > Update Options > Update Now. 3. Install available updates. 4. Restart Excel/computer if prompted.
🔧 Temporary Workarounds
Disable automatic file opening
windowsPrevent Excel from automatically opening files from untrusted sources
Set registry key: HKCU\Software\Microsoft\Office\16.0\Excel\Security\FileValidation to 3
Use Protected View
windowsForce all files from internet to open in Protected View
Set registry key: HKCU\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView to 2
🧯 If You Can't Patch
- Implement application whitelisting to block untrusted Excel files
- Use Microsoft Defender Application Guard for Office to isolate untrusted documents
🔍 How to Verify
Check if Vulnerable:
Check Excel version against patched versions in Microsoft advisoryCheck Version:
In Excel: File > Account > About ExcelVerify Fix Applied:
Verify Excel version matches or exceeds patched version in Microsoft's security update📡 Detection & Monitoring
Log Indicators:
- Excel crash logs with memory access violations
- Event logs showing file opens from untrusted locations
Network Indicators:
- Downloads of Excel files from suspicious sources
SIEM Query:
source="*excel*" AND (event_id=1000 OR keywords="crash" OR "memory")