CVE-2025-29977
📋 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 must deliver the malicious file through email, downloads, or other social engineering methods.
💻 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 the same privileges as the logged-in user, potentially leading to data theft, ransomware deployment, or lateral movement within the network.
Likely Case
Local code execution with user-level privileges, allowing file access, credential harvesting, and installation of additional malware.
If Mitigated
Limited impact if macros are disabled, files are opened in Protected View, or user has limited privileges.
🎯 Exploit Status
Exploitation requires user interaction to open a malicious file. No public exploit code is available at this time.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft's monthly security updates for specific version numbers
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-29977
Restart Required: Yes
Instructions:
1. Open Excel and go to File > Account > Update Options > Update Now. 2. For enterprise deployments, deploy the latest Microsoft security updates through your patch management system. 3. Restart affected systems after patching.
🔧 Temporary Workarounds
Disable automatic opening of Excel files
windowsConfigure Excel to open files in Protected View by default
Set registry key: HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Excel\Security\ProtectedView to 1
Block suspicious Excel file types
allConfigure email gateways and web proxies to block .xls, .xlsx, .xlsm files from untrusted sources
🧯 If You Can't Patch
- Implement application whitelisting to prevent unauthorized Excel execution
- Configure Microsoft Office macro settings to disable all macros with notification
🔍 How to Verify
Check if Vulnerable:
Check Excel version against Microsoft's security bulletin. Vulnerable if running unpatched versions mentioned in advisory.Check Version:
In Excel: File > Account > About Excel (Windows) or Excel > About Excel (macOS)Verify Fix Applied:
Verify Excel version matches or exceeds the patched version specified in Microsoft's advisory.📡 Detection & Monitoring
Log Indicators:
- Excel crash logs with memory access violations
- Windows Event Logs showing Excel process spawning unexpected child processes
Network Indicators:
- Outbound connections from Excel process to suspicious IPs
- DNS requests for known malicious domains from Excel
SIEM Query:
process_name:"EXCEL.EXE" AND (event_id:1000 OR parent_process_name!="explorer.exe")