EUVD-2026-44230
GHSA-px56-54pw-c679
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Client-side file-open memory corruption: local delivery (AV:L) requiring the victim to open a crafted file (UI:R), no prior privileges (PR:N), yielding full code execution in the user context (C:H/I:H/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 (Office 2016 through Office LTSC 2024, Microsoft 365 Apps, Office for Mac, and Office Online Server) allows an attacker to run arbitrary code when a victim opens a maliciously crafted spreadsheet. The flaw is a heap-based buffer overflow (CWE-122) triggered during file parsing, giving full confidentiality, integrity, and availability impact in the user's context. No public exploit identified at time of analysis, and it is not listed in CISA KEV, so exploitation currently appears theoretical rather than active.
Technical ContextAI
The vulnerability lies in Microsoft Excel's parsing of spreadsheet file formats within the Office productivity suite. CWE-122 (heap-based buffer overflow) indicates that Excel writes attacker-controlled data past the bounds of a heap-allocated buffer, typically due to insufficient length validation when deserializing structured records inside a workbook. The CPE data shows the defect is shared across the common Office code base - it affects Microsoft 365 Apps for Enterprise, Excel 2016, Office 2019, Office LTSC 2021/2024, the corresponding Office for Mac and Office LTSC for Mac 2021/2024 builds, and the server-side Office Online Server - indicating the flawed parsing routine resides in a shared Excel/Office component rather than a single edition. A successful overflow corrupts heap metadata or adjacent objects, which a crafted file can steer into control-flow hijacking.
RemediationAI
Patch available per vendor advisory: apply the Microsoft security update referenced in the MSRC Update Guide at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55947, which lists the exact fixed build for each affected edition (Microsoft 365 Apps, Excel 2016, Office 2019, Office LTSC 2021/2024, Office for Mac builds, and Office Online Server); the input does not include a single universal version number because fixes ship per-channel, so consult the advisory for your specific channel and install via Microsoft Update, Click-to-Run auto-update, or WSUS/Intune. For Microsoft 365 Apps and Office for Mac, ensure automatic updates are enabled so the patched build deploys. Where immediate patching is not possible, reduce exposure by opening untrusted spreadsheets in Protected View (block editing until the user explicitly enables it), enforcing Office macro and file-block policies via Group Policy to prevent risky legacy formats from opening, and instructing users not to open Excel attachments from untrusted sources - the trade-off is reduced usability for legitimate external files. For Office Online Server, prioritize the server-side update since it processes documents on behalf of many users.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Heap Overflow
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External POC / Exploit Code
Leaving vuln.today