CVE-2026-55039 Microsoft CVE debrief

Who should care

Users of Microsoft Office Excel, particularly those using 2016, 2019, 2021, and 2024 versions, as well as Microsoft 365 Apps, should apply patches to prevent local code execution. IT administrators and security teams responsible for Microsoft Office Excel and Microsoft 365 Apps deployments should prioritize patching and review system logs for potential exploitation attempts.

Technical summary

The vulnerability, described as an integer underflow (wrap or wraparound), exists in Microsoft Office Excel. Successful exploitation could allow an unauthorized attacker to execute code locally. The CVSS score is 7.8 with a severity of HIGH. The vulnerability is tracked under CWE-122 and CWE-191.

Defensive priority

High priority should be given to patching vulnerable versions of Microsoft Office Excel and Microsoft 365 Apps. IT administrators and security teams should review system logs for potential exploitation attempts and implement compensating controls for exposed systems.

Recommended defensive actions

• Apply patches provided by Microsoft for the affected products.
• Inventory and update vulnerable versions of Microsoft Office Excel and Microsoft 365 Apps.
• Implement compensating controls such as restricting access to sensitive areas for users who cannot immediately patch.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.

Evidence notes

Evidence is based on the CVE record and NVD details. Affected products include various versions of Microsoft Office and Microsoft 365 Apps. Patching is recommended. The CVE record was published on 2026-07-14T18:18:15.257Z and has not been modified since then. The NVD entry is currently Analyzed. Defenders should verify patch deployment and review system logs for potential exploitation attempts.

Official resources