CVE-2026-55058 Details

A vulnerability allowing out-of-bounds read has been identified in Microsoft Office Excel. This issue enables an unauthorized attacker to execute code locally. The vulnerability is present in multiple versions of Microsoft Excel, including Excel 2016 (both 32-bit and 64-bit editions), Excel 2019 (32-bit and 64-bit editions), Office LTSC for Mac 2021, Office LTSC for Mac 2024, and several editions of Microsoft 365 Apps for Enterprise, both for 32-bit and 64-bit systems. The vulnerability arises from improper handling of memory, which could be exploited by an attacker with access to a malicious Office file, requiring the victim to open the file.

Users can download the security update for Microsoft Office 2016, 2019, and various Microsoft 365 Apps editions through the Microsoft Update Catalog. For Office Online Server, the security update is available on the Microsoft Download Center. Instructions for updating Microsoft Office LTSC for Mac 2021 and 2024 can be found on the Microsoft 365 for Mac release notes page.