EUVD-2026-44202
GHSA-vh57-7369-46vq
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
File-based local vector (AV:L) with no privileges but required user interaction to open the document (UI:R); memory-corruption code execution yields full C/I/A impact in the user context.
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 Office Excel (across Microsoft 365 Apps, Office 2016/2019, LTSC 2021/2024, Office for Mac, and Office Online Server) stems from a heap-based buffer overflow (CWE-122) that an attacker triggers when a victim opens a maliciously crafted spreadsheet. Rated CVSS 7.8 with no privileges required but mandatory user interaction, successful exploitation yields full confidentiality, integrity, and availability impact in the context of the victim user. There is no public exploit identified at time of analysis and it is not on the CISA KEV list, but Microsoft has released a patch.
Technical ContextAI
The flaw is a heap-based buffer overflow (CWE-122) in the Excel file-parsing code path, meaning Excel writes past the bounds of a heap-allocated buffer while processing structured spreadsheet content. This class of bug typically arises from unchecked length or count fields in a binary/OOXML record that drive a copy into an undersized allocation, corrupting adjacent heap metadata or object pointers. Because the CPE set spans Microsoft 365 Apps for Enterprise, Excel 2016, Office 2019, Office LTSC 2021/2024, Office 365/LTSC for Mac 2021/2024, and Office Online Server, the vulnerable parsing component is shared across the Excel codebase on both Windows and macOS as well as the server-side rendering product. Heap overflows of this type are frequently leveraged for arbitrary code execution by grooming the heap so that the overflow overwrites a controllable pointer or function table.
RemediationAI
Apply the Microsoft security update for CVE-2026-55137; a patch is available from the vendor and the exact fixed build for each product/channel is published in the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55137 (Patch available per vendor advisory - no single fixed version string was supplied in the input, so cite the per-channel build from the advisory rather than an invented number). Update all affected clients (Microsoft 365 Apps, Office 2016/2019, LTSC 2021/2024, Office for Mac) and Office Online Server. Until patching is complete, reduce exposure by opening untrusted spreadsheets in Protected View and enforcing it via Group Policy (side effect: users must click to enable editing on legitimate files), blocking or quarantining Excel attachments from external senders at the mail gateway, and using Attack Surface Reduction rules and Office macro/hardening policies (side effect: potential friction for users who rely on macros or external file exchange).
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Local code execution in Microsoft Office Word (across Microsoft 365 Apps, Office 2019/LTSC 2021/2024, Office for Mac, an
Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Heap Overflow
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External POC / Exploit Code
Leaving vuln.today