CVE-2026-40367: Microsoft Word Remote Code Execution Vulnerability

Overview

Severity

High (CVSS 8.4)

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Category

Remote Code Execution

Exploit Status

Not Exploited

Exploitation Likelihood

Unlikely

Patch Tuesday

2026-May

Released

2026-05-12

Last Updated

2026-05-20

EPSS Score

0.45% (percentile: 36.1%)

Description

Access of resource using incompatible type ('type confusion') in Microsoft Office Word allows an unauthorized attacker to execute code locally.

FAQ

Is the Attachment Preview Pane an attack vector for this vulnerability? Yes. The attachment Preview Pane that is accessed when a user clicks to preview an attached file is an attack vector; however, the email Preview Pane itself is not. There are multiple update packages available for some of the affected software. Do I need to install all the updates listed in the Security Updates table for the software? Yes. Customers should apply all updates offered for the software installed on their systems. If multiple updates apply, they can be installed in any order. According to the CVSS metric, the attack vector is local (AV:L). Why does the CVE title indicate that this is a remote code execution? The word Remote in the title refers to the location of the attacker. This type of exploit is sometimes referred to as Arbitrary Code Execution (ACE). The attack itself is carried out locally. This means an attacker or victim needs to execute code from the local machine to exploit the vulnerability.

Affected Products (15)

Microsoft Office

• Microsoft SharePoint Enterprise Server 2016
• Microsoft SharePoint Server 2019
• Microsoft Office 2019 for 32-bit editions
• Microsoft Office 2019 for 64-bit editions
• Microsoft 365 Apps for Enterprise for 32-bit Systems
• Microsoft 365 Apps for Enterprise for 64-bit Systems
• Microsoft Office LTSC for Mac 2021
• Microsoft Office LTSC 2021 for 64-bit editions
• Microsoft Office LTSC 2021 for 32-bit editions
• Microsoft SharePoint Server Subscription Edition
• Microsoft Office LTSC 2024 for 32-bit editions
• Microsoft Office LTSC 2024 for 64-bit editions
• Microsoft Office LTSC for Mac 2024
• Microsoft Word 2016 (32-bit edition)
• Microsoft Word 2016 (64-bit edition)

Security Updates (7)

• 5002868
• 5002869
• 5002870
• 5002872
• Release Notes
• 5002863
• 5002858

Acknowledgments

0ccbbf129444eb66344ccafb92b00df4

Revision History

• 2026-05-12: Information published.
• 2026-05-20: The security impact for this vulnerability has been revised from Critical to Important. In addition, the CVSS vector and FAQs were modified. This change does not affect the available security updates. Customers should continue to install the recommended updates to remain protected from this vulnerability.
• 2026-05-20: Today's changes were made in error and have been reverted. This is an informational change only.