CVE-2026-55140 Microsoft CVE debrief

Who should care

Users of Microsoft Office, particularly those using 365 Apps, Office 2016, Office 2019, Office 2021, and Office 2024, should be aware of this vulnerability and take necessary actions to protect themselves. This includes administrators, security teams, and operators who manage and maintain Microsoft Office deployments.

Technical summary

A heap-based buffer overflow vulnerability exists in Microsoft Office, which allows an unauthorized attacker to execute code locally. The vulnerability is caused by improper handling of certain input data, leading to a buffer overflow condition. An attacker can exploit this vulnerability by tricking a user into opening a specially crafted file, potentially leading to arbitrary code execution.

Defensive priority

High

Recommended defensive actions

• Apply patches or updates provided by Microsoft to vulnerable systems
• Implement compensating controls, such as monitoring for suspicious activity
• Conduct regular vulnerability assessments and penetration testing
• Enforce least privilege access and restrict user permissions
• Use secure configuration and change management processes

Evidence notes

The CVE record and NVD detail provide information on the vulnerability, including its CVSS score and vector. Microsoft has provided a patch and vendor advisory for this vulnerability. The vulnerability affects Microsoft Office, particularly those using 365 Apps, Office 2016, Office 2019, Office 2021, and Office 2024. There is no evidence of exploitation in the wild, but defenders should verify the affected scope and severity. The vendor advisory provides guidance on mitigation and remediation.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.