CVE-2026-40364

Code execution via crafted document type confusion

Published May 12, 2026 · Updated May 12, 2026

Type confusion in Microsoft Office Word allows remote attackers to execute code locally when Word processes a crafted document. The affected Word component accesses a resource as an incompatible type, but Microsoft has not disclosed the specific parser or object transition. Processing can occur through Preview Pane without opening the document, and resulting code runs in the affected user's context.

CVSS severity8.4
High
EPSS probability4.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Type confusion in Microsoft Office Word allows remote attackers to execute code locally when Word processes a crafted document. The affected Word component accesses a resource as an incompatible type, but Microsoft has not disclosed the specific parser or object transition. Processing can occur through Preview Pane without opening the document, and resulting code runs in the affected user's context.

The record

CVE
CVE-2026-40364
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Microsoft
Product
Microsoft Office LTSC for Mac 2024
Classifications
CWE-843, CWE-122, CWE-908, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=16.0.0 <16.109.26051019

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Microsoft · Microsoft Office LTSC for Mac 2024version=16.0.0 <16.109.26051019
Microsoft · Microsoft Office 2019version=19.0.0 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft Office LTSC for Mac 2021version=16.0.1 <16.109.26051019
Microsoft · Microsoft Office LTSC 2021version=16.0.1 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft Word 2016version=16.0.1 <16.0.5552.1000
Microsoft · Microsoft Office LTSC 2024version=16.0.0 <https://aka.ms/OfficeSecurityReleases
Microsoft · Microsoft 365 Apps for enterpriseversion=16.0.1 <https://aka.ms/OfficeSecurityReleases

Published CVSS scores

8.4Microsoft CorporationCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-843Access of Resource Using Incompatible Type ('Type Confusion')
CWE-122Heap-based Buffer Overflow
CWE-908Use of Uninitialized Resource
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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