EUVD-2026-56423
GHSA-xc57-cq3p-j9vp
Severity by source
Sources disagree (Medium–Critical)AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
File-based local trigger with mandatory user interaction; no system privileges needed; impact confined to confidentiality with no write or availability consequence.
vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.
CVSS VectorNVD
Lifecycle Timeline
3DescriptionNVD
Out-of-bounds read in Microsoft Office Word allows an unauthorized attacker to disclose information locally.
AnalysisAI
Out-of-bounds read in Microsoft Office Word exposes high-confidentiality memory contents when a user opens a specially crafted document locally. Affected products span Word 2016, Office 2019, Office LTSC 2021/2024, and Microsoft 365 Apps for Enterprise, confirmed via EUVD-2026-56423. No public exploit identified at time of analysis and no CISA KEV listing; vendor patch is available, placing this in the routine-patch-cycle priority tier rather than emergency response.
Technical ContextAI
CWE-125 (Out-of-Bounds Read) occurs when a parsing routine reads beyond an allocated memory buffer, exposing adjacent process memory. In Word's document processing pipeline, a crafted file can trigger this condition during format parsing, causing the application to read and potentially surface memory contents outside the intended data region. Per EUVD-2026-56423, affected products include Microsoft Word 2016 (versions 16.0.1 through below 16.0.5565.1000), Microsoft Office LTSC 2021 (16.0.1+), Microsoft Office LTSC 2024 (16.0.0+), Microsoft 365 Apps for Enterprise (16.0.1+), and Microsoft Office 2019 (19.0.0+). The vulnerability is tagged by the reporter (secure@microsoft.com) as both Information Disclosure and Buffer Overflow, consistent with a read-side memory safety defect rather than a write primitive.
RemediationAI
Apply vendor-released patches immediately. For Microsoft Word 2016, update to build 16.0.5565.1000 or later - this is the only product line with a confirmed specific fixed version number in the available data. For Microsoft Office LTSC 2021, Office LTSC 2024, Microsoft 365 Apps for Enterprise, and Microsoft Office 2019, apply all current updates via the Microsoft Office Security Releases page at https://aka.ms/OfficeSecurityReleases; the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-63521 is the authoritative source for build-level details. Where immediate patching is not possible, enable Microsoft Office Protected View for files originating from the internet or email attachments - this opens documents in a sandboxed read-only mode that restricts the full parsing code paths. Note that Protected View may disrupt editing workflows and users may be prompted to exit it. Restricting inbound delivery of Office documents via email gateway policies reduces attack surface but does not eliminate internal or USB-based delivery vectors.
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Same weakness CWE-125 – Out-of-bounds Read
View allSame technique Buffer Overflow
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External POC / Exploit Code
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