EUVD-2026-56607
GHSA-fp58-2vh9-25hg
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
File-triggered heap overflow requires no privileges but mandates user interaction; full C/I/A reflects arbitrary code execution at user context.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.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 local code execution with full user-level impact when a victim opens a specially crafted document. Affected products span Microsoft 365 Apps for Enterprise, Office LTSC 2021 and 2024 (both Windows and Mac), and Office 365 for Mac. No public exploit identified at time of analysis, and no CISA KEV listing; however, the CVSS 7.8 score and complete C/I/A impact triad reflect the severity of arbitrary code execution achievable through a standard phishing or malicious file delivery scenario.
Technical ContextAI
CWE-122 (Heap-based Buffer Overflow) describes a write operation that places data beyond the allocated bounds of a heap memory buffer. In Microsoft Office Word's document parsing code, processing a maliciously structured file triggers such an overflow, corrupting adjacent heap metadata or function pointers. This class of vulnerability is well-understood and frequently exploitable for code execution on Windows and macOS alike. Affected CPEs span multiple release tracks: Microsoft Office LTSC for Mac 2024 and 2021 (versions below 16.112.26081010), Microsoft 365 Apps for Enterprise (Windows, below the August 2026 release), Microsoft Office LTSC 2024 and 2021 for Windows (below the August 2026 release), and Microsoft Office 365 for Mac (below 16.112.26081010). The vulnerability is confirmed by the MSRC advisory (EUVD-2026-56607) and reported through Microsoft's own security disclosure address (secure@microsoft.com).
RemediationAI
Apply the vendor-released patch immediately. For macOS users on any affected Office track (LTSC 2024, LTSC 2021, or 365 for Mac), update to version 16.112.26081010 or later via Microsoft AutoUpdate or the Mac App Store. For Windows users on Microsoft 365 Apps for Enterprise, Office LTSC 2021, or Office LTSC 2024, apply the August 2026 cumulative update available at https://aka.ms/OfficeSecurityReleases and through Windows Update or WSUS. As a compensating control where immediate patching is not feasible, consider enabling Microsoft Office Protected View so documents received from the internet or email open in read-only sandboxed mode - this prevents active content and parsing of complex document structures until the user explicitly enables editing, blocking the exploit trigger. Note that Protected View can be bypassed by users and does not apply to files opened from trusted locations. Disabling macros via Group Policy is not a mitigation here, as this is a parser-level heap overflow, not a macro-based attack.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
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