CVE-2025-29979
📋 TL;DR
A heap-based buffer overflow vulnerability in Microsoft Office Excel allows attackers to execute arbitrary code on affected systems by tricking users into opening malicious Excel files. This affects all users running vulnerable versions of Microsoft Excel. The vulnerability requires user interaction but can lead to full system compromise.
💻 Affected Systems
- Microsoft Excel
- Microsoft Office
- Microsoft 365 Apps
📦 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
Complete system takeover with administrative privileges, data exfiltration, ransomware deployment, and lateral movement within the network.
Likely Case
Local privilege escalation leading to data theft, malware installation, and persistence mechanisms on the compromised workstation.
If Mitigated
Limited impact with proper application sandboxing, restricted user privileges, and network segmentation preventing lateral movement.
🎯 Exploit Status
Requires user interaction to open malicious Excel file. Heap-based buffer overflows typically require precise memory manipulation but are commonly exploited.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update Guide for specific version numbers
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-29979
Restart Required: Yes
Instructions:
1. Open any Office application. 2. Go to File > Account > Update Options > Update Now. 3. Restart computer after update completes. 4. For enterprise deployments, use Microsoft Update Catalog or WSUS to deploy patches.
🔧 Temporary Workarounds
Block Excel file execution via Group Policy
windowsPrevent Excel from opening files from untrusted sources using application control policies
Use Group Policy Editor to configure Software Restriction Policies or AppLocker rules for Excel
Enable Protected View for all Excel files
windowsForce Excel to open all files in Protected View to prevent automatic code execution
Excel Options > Trust Center > Trust Center Settings > Protected View > Enable all Protected View options
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized Excel execution
- Use email filtering to block Excel attachments and enforce user training against opening suspicious files
🔍 How to Verify
Check if Vulnerable:
Check Excel version via File > Account > About Excel and compare with Microsoft's patched version listCheck Version:
powershell Get-ItemProperty "HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*" | Where {$_.DisplayName -like "*Excel*"} | Select DisplayName, DisplayVersionVerify Fix Applied:
Verify Office updates are installed via Control Panel > Programs > Programs and Features > View installed updates📡 Detection & Monitoring
Log Indicators:
- Windows Event Logs: Application crashes of EXCEL.EXE with exception codes like 0xC0000005
- Process creation from Excel with unusual command lines or child processes
Network Indicators:
- Outbound connections from Excel process to suspicious IPs
- DNS requests for command and control domains originating from Excel
SIEM Query:
source="windows" process_name="EXCEL.EXE" (event_id=1000 OR event_id=1001) exception_code="0xC0000005"