CVE-2026-81959

Microsoft Excel is like a spreadsheet “engine” that opens and processes files. This vulnerability is a flaw in that engine that can be triggered by a specially made Excel file, which can cause the computer to run attacker code when the file is opened.

This matters if your business uses Microsoft Excel or Microsoft Office products such as Microsoft 365 Apps, Microsoft Excel, or Office 2016/2019/2021/2024 (including Mac variants). The risk is tied to opening a malicious Excel file—so it’s most relevant on devices where people receive or download Office files, and only if an attacker can reach users with a crafted file (it’s not about someone being “authenticated” inside your network).

Treat this as urgent because it affects a common workplace application and the impact is full code execution on the user’s machine. Even though there’s no listing in CISA’s KEV feed and no public exploit code is recorded, the vulnerability has clear potential for real-world harm when users open malicious attachments, and Microsoft has already provided fixed versions.