CVE-2026-55949

Analyzed Analyzed - Analysis Complete

Use of Uninitialized Resource in Microsoft Office Excel Allows Local Code Execution

Publication date: 2026-07-14

Last updated on: 2026-07-15

Assigner: Microsoft Corporation

Description

Use of uninitialized resource in Microsoft Office Excel allows an unauthorized attacker to execute code locally.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-07-14

Last Modified

2026-07-15

Generated

2026-08-04

AI Q&A

2026-07-15

EPSS Evaluated

2026-08-02

NVD

CVE-2026-55949

EUVD

EUVD-2026-44231

Affected Vendors & Products

Vendor	Product	Version / Range
microsoft	365_apps	*
microsoft	365_apps	*
microsoft	excel	2016
microsoft	excel	2016
microsoft	office_2019	*
microsoft	office_2019	*
microsoft	microsoft_365	*
microsoft	office_2021	*
microsoft	office_2021	*
microsoft	office_2021	*
microsoft	office_2024	*
microsoft	office_2024	*
microsoft	office_2024	*
microsoft	office_online_server	to 16.0.10417.20175 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-908	The product uses or accesses a resource that has not been initialized.

Attack-Flow Graph

Executive Summary

This vulnerability involves the use of an uninitialized resource in Microsoft Office Excel. An attacker could exploit this to execute code locally on an affected system.

Detection Guidance

Detection of this vulnerability requires monitoring for unusual Excel file processing or code execution attempts. Check for suspicious processes spawned by Excel, unexpected network connections, or files with malformed structures. Use tools like Process Explorer or Windows Event Viewer to inspect Excel-related activities. Ensure your antivirus definitions are updated to detect known exploit patterns.

Impact Analysis

An unauthorized attacker could run malicious code on your system, potentially leading to data theft, system damage, or unauthorized access. This could affect files, applications, or even the entire operating system.

Compliance Impact

This vulnerability could lead to unauthorized access or data breaches, which may violate compliance requirements such as GDPR or HIPAA. Organizations must address it to maintain data protection standards.

Mitigation Strategies

Apply the latest security updates from Microsoft for affected Office products immediately. Disable Excel macros if not required and restrict user permissions to minimize attack surface.

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