EUVD-2026-44203
GHSA-q5m6-w3x7-pm25
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Local file-parsing overflow needing victim to open a crafted document (AV:L, UI:R), no attacker privileges (PR:N), yielding full code execution in user context (C/I/A:H).
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
AnalysisAI
Local code execution in Microsoft Excel arises from a heap-based buffer overflow (CWE-122) that an attacker triggers by luring a victim into opening a maliciously crafted spreadsheet, yielding attacker code in the user's security context. It affects a broad Office family including Microsoft 365 Apps for Enterprise, Excel 2016, Office 2019, Office LTSC 2021/2024, the macOS editions, and Office Online Server. The CVSS 3.1 base score is 7.8 and the vector requires user interaction (UI:R); there is no public exploit identified at time of analysis and it is not listed in CISA KEV.
Technical ContextAI
The flaw is a heap-based buffer overflow (CWE-122), a memory-corruption class in which parsing routines write past the bounds of a dynamically allocated heap buffer, corrupting adjacent heap metadata or object pointers that can be manipulated into control-flow hijack. Here the vulnerable component is Excel's spreadsheet file parser, reached whenever a document is opened by the application. The CPE set - cpe:2.3:a:microsoft:microsoft_365_apps_for_enterprise, microsoft_excel_2016, microsoft_office_2019, office_365_for_mac, office_ltsc_2021, office_ltsc_2024, office_ltsc_for_mac_2021, office_ltsc_for_mac_2024, and office_online_server - shows the shared Office/Excel parsing engine is affected across both Windows and macOS builds and even the server-side Office Online Server rendering component.
RemediationAI
Patch available per vendor advisory - apply the Microsoft update for CVE-2026-55053 documented at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55053, ensuring Microsoft 365 Apps, Office 2019/2016, the LTSC 2021/2024 channels, the macOS editions, and Office Online Server all receive their respective fixed builds; the input does not specify an exact fixed version number, so pull the precise build from the MSRC guide per product/channel. Where immediate patching is not possible, reduce exposure by opening untrusted spreadsheets in Protected View and keeping it enabled (trade-off: users must click to exit Protected View for legitimate editing), blocking or quarantining Excel attachments from external senders at the mail gateway, and enabling Attack Surface Reduction rules and Office macro/hardening baselines. These controls reduce but do not eliminate risk, since the overflow is in file parsing rather than macros.
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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
Leaving vuln.today