EUVD-2026-44180
GHSA-h63h-p87q-mppp
Severity by source
AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
File must be opened locally by the user (AV:L, UI:R) with no attacker privileges (PR:N); memory-corruption RCE in user context yields full C/I/A impact, scope unchanged.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Lifecycle Timeline
2DescriptionCVE.org
Integer underflow (wrap or wraparound) in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
AnalysisAI
Local code execution in Microsoft Excel (and the broader Office suite through Microsoft 365 Apps, Office 2019/2021/2024 LTSC, Office for Mac, and Office Online Server) arises from an integer underflow (CWE-191) in Excel's file parsing, letting an attacker run arbitrary code in the context of the user who opens a maliciously crafted spreadsheet. The CVSS 3.1 vector (AV:L/AC:L/PR:N/UI:R) shows no attacker privileges are needed but the victim must open the file, giving full confidentiality, integrity, and availability impact. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the victim to open an attacker-supplied malicious Excel file (CVSS UI:R), and code runs only in the context and privilege level of that user - there is no remote or unauthenticated network trigger (AV:L). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | This is a moderately high but not emergency-tier risk. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker emails or shares a specially crafted Excel workbook that embeds malformed size/length fields; when the targeted user opens it in a vulnerable Office build, the integer underflow corrupts memory and executes attacker-supplied code with that user's privileges. No public exploit is identified at time of analysis, and the local vector with required user interaction means the attack hinges on successful social engineering rather than remote automation. |
| Remediation | Patch available per vendor advisory - apply the Microsoft security update for Office referenced at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55039; the input does not list exact patched build numbers, so consult that advisory for the specific version per channel (Click-to-Run/Current, Monthly Enterprise, LTSC MSI, and Mac builds), and update Office Online Server on the server side. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Identify all systems running Microsoft Excel and Office products in your environment and assess which users routinely access externally-sourced or untrusted spreadsheets. …
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Same weakness CWE-191 – Integer Underflow
View allSame technique Authentication Bypass
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External POC / Exploit Code
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