CVE-2025-27751
📋 TL;DR
A use-after-free vulnerability in Microsoft Office Excel allows attackers to execute arbitrary code on a victim's system by tricking them into opening a malicious Excel file. This affects all users running vulnerable versions of Microsoft Excel. The attacker gains the same privileges as the logged-in user.
💻 Affected Systems
- Microsoft Excel
📦 What is this software?
365 Apps by Microsoft
Excel 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 →
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise with attacker gaining complete control over the victim's computer, potentially leading to data theft, ransomware deployment, or lateral movement within the network.
Likely Case
Local code execution with user privileges, allowing attackers to steal sensitive documents, install malware, or establish persistence on the system.
If Mitigated
Limited impact if user runs with minimal privileges, application sandboxing is enabled, and macro execution is disabled by default.
🎯 Exploit Status
Requires social engineering to deliver malicious file; exploitation depends on memory manipulation techniques
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update Guide for specific patch versions
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-27751
Restart Required: Yes
Instructions:
1. Open Microsoft Excel
2. Go to File > Account > Update Options
3. Select 'Update Now'
4. Restart Excel when prompted
5. Alternatively, install updates through Windows Update
🔧 Temporary Workarounds
Disable automatic opening of Excel files
windowsPrevent Excel from automatically opening files from untrusted sources
Not applicable - configure through Excel/Windows settings
Use Protected View
windowsEnsure Excel opens files from internet in Protected View by default
File > Options > Trust Center > Trust Center Settings > Protected View > Enable all options
🧯 If You Can't Patch
- Restrict Excel file execution to trusted sources only
- Implement application whitelisting to prevent unauthorized Excel execution
🔍 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 is updated to patched version and test with known safe files📡 Detection & Monitoring
Log Indicators:
- Excel crash logs with memory access violations
- Unexpected Excel process spawning child processes
Network Indicators:
- Unusual outbound connections from Excel process
SIEM Query:
Process creation where parent_process contains 'excel.exe' AND command_line contains suspicious patterns