CVE-2026-26144
📋 TL;DR
This cross-site scripting (XSS) vulnerability in Microsoft Office Excel allows attackers to inject malicious scripts into Excel files. When a user opens a specially crafted Excel document, the attacker can steal sensitive information like session cookies or credentials. This affects all users who open untrusted Excel files with vulnerable versions.
💻 Affected Systems
- Microsoft Office Excel
⚠️ 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
Attacker steals administrator credentials, gains full access to internal systems, and exfiltrates sensitive data.
Likely Case
Attacker steals user session cookies or credentials, leading to unauthorized access to web applications or email accounts.
If Mitigated
Limited impact due to proper file validation, network segmentation, and least privilege access controls.
🎯 Exploit Status
Exploitation requires user interaction (opening a malicious Excel file). No public exploit code available yet.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Microsoft Security Update Guide for specific version
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26144
Restart Required: Yes
Instructions:
1. Open any Office application. 2. Go to File > Account > Update Options > Update Now. 3. Restart computer after update completes.
🔧 Temporary Workarounds
Disable Active Content in Excel
windowsPrevents execution of scripts in Excel files
Excel Options > Trust Center > Trust Center Settings > Macro Settings > Disable all macros without notification
Use Protected View
windowsOpen untrusted files in read-only Protected View mode
Excel Options > Trust Center > Trust Center Settings > Protected View > Enable all Protected View settings
🧯 If You Can't Patch
- Block Excel files from untrusted sources at email gateways and web proxies
- Implement application whitelisting to restrict which Excel files can execute scripts
🔍 How to Verify
Check if Vulnerable:
Check Excel version against patched versions in Microsoft advisoryCheck Version:
Excel: File > Account > About Excel (Windows) or Excel > About Excel (macOS)Verify Fix Applied:
Verify Excel version is updated to patched version and test with known safe files📡 Detection & Monitoring
Log Indicators:
- Excel crash logs with script-related errors
- Unusual file access patterns from Excel processes
Network Indicators:
- Outbound connections to unknown domains after opening Excel files
- Unexpected data exfiltration from workstations
SIEM Query:
source="windows-security" EventID=4688 | where process_name contains "EXCEL.EXE" | where command_line contains suspicious strings