Out-of-bounds Read in Microsoft Office

Executive Summary

CVE-2026-55028 is an out-of-bounds read vulnerability in Microsoft Office. This flaw allows an unauthorized attacker to access and disclose sensitive information locally on the affected system.

An out-of-bounds read occurs when a program reads data beyond the intended boundary of a buffer or memory location. In this case, the vulnerability could be exploited by an attacker to read memory contents that should not be accessible, leading to information disclosure.

The CVSS v3.1 score for this vulnerability is 5.5, with a vector of AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N. This indicates the attack requires local access, low attack complexity, no privileges, and user interaction (such as opening a malicious file). The impact is high confidentiality loss with no integrity or availability impact.

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Detection Guidance

The provided context does not include specific detection methods or commands for identifying the presence of CVE-2026-55028 on a network or system. Detection typically involves checking for vulnerable versions of Microsoft Office or using security tools that can identify out-of-bounds read vulnerabilities in installed software.

To detect vulnerable versions of Microsoft Office, you may use system inventory tools or scripts to check installed versions. For example, on Windows systems, you can use PowerShell commands to list installed software:

• Get-WmiObject -Class Win32_Product | Where-Object {$_.Name -like "*Microsoft Office*"} | Select-Object Name, Version

Additionally, Microsoft may provide detection guidance or updates in their security advisories, which can be found in Resource 1.

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Impact Analysis

This vulnerability can impact you in several ways if you use Microsoft Office on an affected system.

• An attacker could exploit this flaw to access sensitive information stored in memory, such as documents, credentials, or other confidential data.
• The attacker must have local access to the system or trick a user into opening a malicious file, which could lead to unauthorized data exposure.
• While the vulnerability does not allow remote code execution or system takeover, the disclosed information could be used for further attacks or identity theft.

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Compliance Impact

This vulnerability could affect compliance with data protection regulations and standards in the following ways.

• GDPR (General Data Protection Regulation): If the disclosed information includes personal data of EU citizens, this could constitute a data breach under GDPR. Organizations may be required to report the incident and could face fines if they failed to implement adequate security measures.
• HIPAA (Health Insurance Portability and Accountability Act): If the vulnerability leads to the exposure of protected health information (PHI), it could result in a HIPAA violation. Covered entities must ensure the confidentiality of PHI, and a breach could lead to penalties.
• Other standards (e.g., ISO 27001, NIST): Organizations adhering to these frameworks may need to assess the vulnerability as part of their risk management processes. Failure to patch or mitigate the issue could result in non-compliance with security controls.

To maintain compliance, organizations should apply the available security updates for Microsoft Office and monitor for any unauthorized access or data exposure.

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Mitigation Strategies

Based on the provided context, the following immediate steps are recommended to mitigate CVE-2026-55028:

• Apply the latest security updates provided by Microsoft for Microsoft Office. Refer to the Microsoft Update Guide (Resource 1) for the specific patch addressing this vulnerability.
• Restrict local access to systems running vulnerable versions of Microsoft Office to trusted users only, as the vulnerability requires local access (AV:L in the CVSS vector).
• Monitor Microsoft's security advisories for additional guidance or workarounds if a patch is not immediately available.
• Consider implementing application whitelisting or other security controls to limit the execution of unauthorized or vulnerable software.

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