EUVD-2026-56709
GHSA-4hxm-v7c3-w944
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Local vector and UI:R reflect file-open trigger; PR:N because no authenticated session is required to open a document; full C/I/A impact follows from arbitrary code execution.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Stack-based buffer overflow in Microsoft Office Word allows an unauthorized attacker to execute code locally.
AnalysisAI
Stack-based buffer overflow in Microsoft Office Word enables local arbitrary code execution when a user opens a maliciously crafted document. Affected products span Word 2016 through Microsoft 365 Apps for Enterprise and LTSC 2021/2024 on both Windows and macOS. No public exploit identified at time of analysis, but Microsoft has released patches across all affected product lines via the August 2026 security update cycle.
Technical ContextAI
The vulnerability is a stack-based buffer overflow (CWE-121) in Microsoft Office Word's document parsing engine. Stack-based overflows occur when data written to a stack-allocated buffer exceeds its declared size, corrupting adjacent stack memory including saved return addresses and frame pointers, which an attacker can leverage to redirect execution to attacker-controlled code. The CWE-121 class is a well-understood exploit primitive in native code parsers. The EUVD-sourced CPE data confirms affected products span Microsoft Word 2016 (Windows), Microsoft Office 2019, LTSC 2021, LTSC 2024 (Windows), Microsoft Office 365 for Mac, LTSC 2021 for Mac, and LTSC 2024 for Mac - indicating the vulnerable parsing code is present in a shared component across both Windows and macOS Office builds.
RemediationAI
The primary fix is to apply Microsoft's August 2026 security update for all affected Office products. For macOS users, update to build 16.112.26081010 or later, which covers Office 365 for Mac, Office LTSC for Mac 2021, and Office LTSC for Mac 2024. For Microsoft Word 2016 on Windows, update to build 16.0.5565.1000 or later. For Office 2019, LTSC 2021, LTSC 2024, and Microsoft 365 Apps for Enterprise on Windows, consult https://aka.ms/OfficeSecurityReleases for the exact patched build numbers. Updates are available via Microsoft Update, Windows Update for Business, and the Microsoft 365 admin center. As a compensating control where patching cannot be applied immediately, consider enabling Microsoft Office Protected View and disabling automatic document opening from untrusted sources - note that Protected View limits document editing and may impact productivity. Additionally, blocking delivery of Office document attachments at the email gateway for users who do not require them reduces the exposure surface. Mark-of-the-Web (MOTW) enforcement in Office should remain enabled as it triggers Protected View for internet-sourced files.
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Same weakness CWE-121 – Stack-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today