CVE-2026-78511: CWE-122: Heap-based Buffer Overflow in Microsoft Microsoft 365 Apps for Enterprise

This vulnerability (CVE-2026-78511) involves a heap-based buffer overflow in Microsoft Office Word, part of Microsoft 365 Apps for Enterprise. It enables remote code execution by an unauthorized attacker over a network. The CVSS 3.1 base score is 8.8, indicating high severity with network attack vector, low attack complexity, no privileges required, user interaction required, and high impact on confidentiality, integrity, and availability. Multiple version ranges of Microsoft 365 Apps for Enterprise are affected, with official patches released by Microsoft. The vendor advisory confirms the availability of an official fix and that remediation is managed by Microsoft for this cloud service.

Successful exploitation of this vulnerability could allow an attacker to execute arbitrary code remotely on a vulnerable system, potentially leading to full compromise of confidentiality, integrity, and availability of the affected application and system. The vulnerability requires user interaction but no privileges or authentication. No known active exploits have been reported.

An official fix is available from Microsoft. Users and administrators should apply the latest updates for Microsoft 365 Apps for Enterprise as provided in the Microsoft Security Response Center advisory. Since this is a cloud-hosted service, Microsoft manages remediation server-side. Check the vendor advisory for the latest patch status and deployment guidance.