CVE-2026-81398: CWE-122: Heap-based Buffer Overflow in Microsoft Microsoft 365 Apps for Enterprise

This vulnerability (CVE-2026-81398) involves a heap-based buffer overflow in Microsoft Office Excel, part of Microsoft 365 Apps for Enterprise. The flaw enables an unauthorized attacker to execute code locally, potentially leading to full compromise of confidentiality, integrity, and availability. The CVSS 3.1 vector indicates local attack vector with low complexity, no privileges required, but user interaction is needed. Microsoft has published an official fix and manages remediation for this cloud service. Multiple affected version ranges are identified, all versions prior to specific fixed builds.

Successful exploitation allows an unauthorized attacker to execute arbitrary code locally, resulting in high impact on confidentiality, integrity, and availability of the affected system. This could lead to full system compromise if exploited.

An official fix is available from Microsoft. Users and administrators should apply the security updates provided by Microsoft as detailed in the vendor advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-81398. Since this is a cloud-hosted service, Microsoft manages remediation server-side. There are no known active exploits, so applying the official patch is the recommended action.