EUVD-2026-56420
GHSA-632h-4gq8-hc2m
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
AV:L reflects file-based delivery requiring local rendering; PR:N because no account privileges are needed; UI:R because victim must open the crafted document; full C/I/A impact confirmed by code execution outcome.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Out-of-bounds read in Microsoft Office allows an unauthorized attacker to execute code locally.
AnalysisAI
Out-of-bounds read (CWE-125) in Microsoft Office enables local code execution across a broad range of Office product editions on both Windows and macOS. The CVSS vector (AV:L/AC:L/PR:N/UI:R) confirms the attack requires no privileges but does require a victim to open a crafted file, consistent with a malicious document delivery scenario. A patch has been released by Microsoft; no public exploit code or CISA KEV listing has been identified at the time of analysis, though the full CIA impact (C:H/I:H/A:H) and breadth of affected products make this a high-priority patching target for enterprise environments.
Technical ContextAI
CWE-125 (Out-of-Bounds Read) occurs when software reads memory past the end of an allocated buffer. While typically associated with information disclosure, this class of flaw can be exploited for code execution when attacker-controlled data influences program flow or when the read primitive is chained with memory layout knowledge. The CVSS vector's S:U (no scope change) and full C/I/A impact indicate that exploitation achieves code execution within the Office process context. The vulnerability affects the Microsoft Office document parsing subsystem across LTSC and subscription editions, spanning both Windows (Office 2016 through LTSC 2024, Microsoft 365 Apps for Enterprise) and macOS (Office LTSC for Mac 2021/2024, Microsoft 365 for Mac). Affected CPE ranges inferred from EUVD-2026-56420 data include builds as old as 16.0.0 (Office 2016/LTSC 2024) and 16.0.1 (LTSC 2021/M365). The tags 'Information Disclosure' and 'Buffer Overflow' from ENISA align with the OOB read root cause and its code execution consequence.
RemediationAI
Apply the vendor-released patch immediately. For macOS editions (Office LTSC for Mac 2024, LTSC for Mac 2021, and Microsoft 365 for Mac), update to build 16.112.26081010 or later via Microsoft AutoUpdate or your MDM solution. For Microsoft Office 2016 on Windows, update to build 16.0.5565.1001 or later. For all other Windows editions - Office 2019, Office LTSC 2021, Office LTSC 2024, and Microsoft 365 Apps for Enterprise - consult https://aka.ms/OfficeSecurityReleases for the exact fixed build, as specific version numbers were not independently confirmed in the available data. If immediate patching is not feasible, consider blocking delivery of Office documents from untrusted external sources at the email gateway and disabling macro execution and external content fetching as compensating controls - note that these do not neutralize the OOB read in the parser itself and should not substitute for patching. Restricting Office process execution via attack surface reduction (ASR) rules in Microsoft Defender can limit post-exploitation lateral movement but does not prevent initial code execution.
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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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