This vulnerability (CVE-2026-55029) is a heap-based buffer overflow in Microsoft Office Excel component of Microsoft 365 Apps for Enterprise. It enables an unauthorized attacker to execute arbitrary code locally. The CVSS 3.1 score is 7.8 (high severity) with vector AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H, indicating local attack vector with low complexity, no privileges required, user interaction needed, and high impact on confidentiality, integrity, and availability. Microsoft has published an official fix and manages remediation for this cloud service. The affected version explicitly stated is 16.0.1.

Successful exploitation allows an unauthorized attacker to execute arbitrary code locally on the affected system, potentially leading to full compromise of confidentiality, integrity, and availability of the affected Microsoft 365 Apps for Enterprise environment. This can result in unauthorized data access, modification, or denial of service.

An official fix is available from Microsoft. Since this is a cloud-hosted service, Microsoft manages remediation server-side. Users and administrators should ensure their Microsoft 365 Apps for Enterprise are updated according to the vendor advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55029 to apply the patch.