What is the CVSS score of EUVD-2026-56422?

EUVD-2026-56422 has a CVSS 3.1 base score of 7.8 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.4%.

Which versions of Microsoft Office Word are affected by EUVD-2026-56422?

A heap-based buffer overflow in Microsoft Office Word (affecting Office LTSC 2021/2024, Office 2019, Microsoft 365 Apps, Office 365 for Mac, and Outlook 2016) enables arbitrary local code execution…. A patch is available.

How to fix or mitigate EUVD-2026-56422?

Within 24 hours, inventory all affected Office installations across the organization (Office LTSC 2021/2024, Office 2019, Microsoft 365 Apps for Enterprise, Office 365 for Mac, and Outlook 2016) and identify systems with the highest email exposure. Within 7 days, deploy the vendor-released patch to systems where users frequently interact with external documents (executives, HR, customer-facing teams, and financial departments). Complete full deployment of the vendor patch across all affected Office instances within 30 days, prioritizing critical business functions and high-value user populations.

Microsoft Office Word EUVD-2026-56422

| CVE-2026-63518 HIGH

Heap-based Buffer Overflow (CWE-122)

2026-08-11 secure@microsoft.com

GHSA-mvf6-42fg-9rcw

Buffer Overflow Heap Overflow Microsoft 365 Apps Word Microsoft 365 Office 2021 Office 2024 Office 2019

7.8

CVSS 3.1 · Vendor: microsoft

Severity by source

Vendor (microsoft) PRIMARY

7.8 HIGH

AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

ENISA EUVD

CRITICAL

qualitative

vuln.today AI

7.8 HIGH

AV:L reflects file-based triggering requiring local document open; UI:R because victim must open the crafted file; PR:N as the attacker needs no prior system access; full C/I/A impact consistent with arbitrary code execution.

3.1 AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

4.0 AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (microsoft).

CVSS VectorVendor: microsoft

Attack Vector

Local

Attack Complexity

Low

Privileges Required

None

User Interaction

Required

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Generated

Aug 11, 2026 - 18:52 vuln.today

Patch available

Aug 11, 2026 - 18:19 EUVD

CVE Published

Aug 11, 2026 - 17:18 nvd

HIGH 7.8

DescriptionCVE.org

Heap-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code locally.

AnalysisAI

Heap-based buffer overflow in Microsoft Office Word enables arbitrary local code execution when a user opens a specially crafted document. The vulnerability spans a broad set of affected products across both Windows and macOS platforms, including Office LTSC 2021/2024, Office 2019, Microsoft 365 Apps for Enterprise, Office 365 for Mac, and Outlook 2016. No public exploit code has been identified at time of analysis, though Microsoft has released a patch and the document-based delivery model is a proven and widely abused attack vector in enterprise phishing campaigns.

Technical ContextAI

CWE-122 (Heap-based Buffer Overflow) describes a condition where a write operation exceeds the bounds of a heap-allocated buffer, corrupting adjacent memory - which can include heap metadata, vtable pointers, or adjacent object data - and redirect program execution to attacker-controlled code. The vulnerability resides in Microsoft Word's document parsing engine. The presence of both Windows and macOS product families in the affected version list (including Office LTSC for Mac and Office 365 for Mac) indicates the vulnerable code is present in a shared or cross-platform component of Word's file-handling logic. Outlook 2016's inclusion suggests it is affected through its integration with Word for document composition or preview rendering. The CVSS vector AV:L/UI:R is consistent with a crafted-file attack: the overflow is triggered during parsing of a malicious document when a local user opens it.

RemediationAI

Apply Microsoft's patch immediately via the standard Office update channel. For Windows-based products - Office LTSC 2021, LTSC 2024, Office 2019, and Microsoft 365 Apps for Enterprise - updates are available through https://aka.ms/OfficeSecurityReleases. For macOS-based products - Office 365 for Mac, LTSC for Mac 2021, and LTSC for Mac 2024 - update to version 16.112.26081010 or later. For Microsoft Outlook 2016, update to version 16.0.5565.1000 or later. Where immediate patching is not feasible, ensure Office Protected View is configured to open documents received from the internet or email attachments in read-only mode, reducing but not eliminating the attack surface; note that Protected View can be bypassed by social engineering that induces users to enable editing. Enabling Microsoft's Attack Surface Reduction rule 'Block Office applications from creating child processes' (GUID: d4f940ab-401b-4efc-aadc-ad5f3c50688a) can limit post-exploitation impact by preventing the spawned process from launching secondary payloads, though this may affect legitimate Office automation workflows.