CVE-2026-26109
📋 TL;DR
This vulnerability allows an attacker to read memory outside the intended buffer in Microsoft Excel, potentially leading to information disclosure or remote code execution. Users who open malicious Excel files are affected, particularly organizations using vulnerable versions of Microsoft Office.
💻 Affected Systems
- Microsoft Excel
- Microsoft Office
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise via arbitrary code execution with the privileges of the user opening the malicious Excel file.
Likely Case
Information disclosure or application crash when users open specially crafted Excel files.
If Mitigated
Limited impact with proper file validation and user awareness training.
🎯 Exploit Status
Exploitation requires user interaction to open a malicious Excel file. No public exploit code is currently available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update for specific version
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26109
Restart Required: Yes
Instructions:
1. Open Microsoft Excel
2. Go to File > Account > Update Options
3. Select 'Update Now'
4. Restart Excel when prompted
🔧 Temporary Workarounds
Disable Excel file opening
windowsPrevent Excel from opening files from untrusted sources
Use Protected View
windowsConfigure Excel to always open files from internet in Protected View
Excel Options > Trust Center > Trust Center Settings > Protected View > Enable all options
🧯 If You Can't Patch
- Implement application whitelisting to block unauthorized Excel execution
- Use email filtering to block suspicious Excel attachments
🔍 How to Verify
Check if Vulnerable:
Check Excel version against Microsoft's security advisory for affected versionsCheck Version:
In Excel: File > Account > About ExcelVerify Fix Applied:
Verify Excel has been updated to 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 termination
Network Indicators:
- Unusual Excel file downloads from external sources
- Excel files with abnormal file sizes or extensions
SIEM Query:
source="windows" event_id=1000 process_name="EXCEL.EXE" | search "access violation" OR "out of bounds"