CVE-2026-100210 – Microsoft Office Excel Remote Code Execution Vulnerability

Microsoft has addressed a Critical Remote Code Execution (RCE) vulnerability in Microsoft Office Excel that could allow an unauthorized attacker to execute malicious code on a vulnerable system. The vulnerability, tracked as CVE-2026-100210, is caused by a heap-based buffer overflow that can be triggered when a user opens a specially crafted Office file. An attacker could exploit this weakness by convincing a user to open a malicious document, potentially compromising sensitive information, modifying files, or disrupting business operations. Although exploitation is currently considered less likely, the vulnerability carries a high potential impact because attackers do not need existing privileges to initiate an attack.

CVSS SCORE: 8.8

SEVERITY: Critical

Threat

This vulnerability presents a significant security risk because it allows attackers to target Microsoft Office Excel users through malicious Office documents.

An attacker could distribute a specially crafted Excel file through email, file-sharing platforms, or other communication channels and persuade an employee to open it.

Successful exploitation could allow an attacker to:

• Execute malicious code on the affected system.
• Access confidential business information.
• Modify or delete important files.
• Install malware or other malicious software.
• Disrupt business operations by compromising affected systems.

The vulnerability has low attack complexity and requires no existing privileges, making it particularly concerning in environments where employees frequently exchange Office documents.

However, exploitation requires user interaction, meaning an attacker must convince the intended victim to open the malicious file.

Exploits

Publicly Disclosed: No

Exploited in the Wild: No

Exploit Code Maturity: Unproven

Exploitability Assessment: Exploitation Less Likely

There are currently no confirmed reports of this vulnerability being actively exploited in the wild.

The vulnerability has not been publicly disclosed, and exploit code maturity is classified as unproven.

The existence of publicly available proof-of-concept (PoC) exploit code cannot be confirmed.

Although active exploitation has not been identified, the vulnerability could become an attractive target because it affects widely used Microsoft Office products and allows remote code execution.

Technical Summary

CVE-2026-100210 is a heap-based buffer overflow vulnerability (CWE-122) affecting Microsoft Office Excel.

A heap-based buffer overflow occurs when an application writes more data into a memory buffer than the allocated space can safely accommodate.

This can corrupt adjacent memory and potentially allow an attacker to influence application execution.

In this case, an attacker could exploit the vulnerability by creating a specially crafted Microsoft Office document designed to trigger the memory corruption condition.

The attack process involves the following:

1. An attacker prepares a malicious Office file containing specially crafted content.

2. The attacker sends the document to a targeted user.

3. The attacker convinces the user to open the file using a vulnerable Microsoft Office application.

4. Processing the malicious content could trigger the heap-based buffer overflow.

5. Successful exploitation could allow unauthorized code execution on the affected system.

The vulnerability has the following technical characteristics:

• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Unchanged
• Confidentiality Impact: High
• Integrity Impact: High
• Availability Impact: High

The vulnerability does not require an attacker to have an existing account or elevated privileges.

However, the attacker must convince a user to open the malicious Office document.

Microsoft has also confirmed that the Preview Pane is not an attack vector for this vulnerability.

Successful exploitation could compromise the confidentiality, integrity, and availability of information on the affected system.

Exploitability

The vulnerability affects the following Microsoft products:

• Microsoft 365 Apps for Enterprise (32-bit and 64-bit)
• Microsoft Office 365 for Mac
• Microsoft Office LTSC 2021 (32-bit and 64-bit)
• Microsoft Office LTSC 2024 (32-bit and 64-bit)
• Microsoft Office LTSC for Mac 2021
• Microsoft Office LTSC for Mac 2024
• Office Online Server

Office Online Server Security Update: KB5002928

The specific affected build numbers are not confirmed.

An attacker could exploit this vulnerability by sending a malicious Office document and convincing the targeted user to open it.

No prior privileges are required, but user interaction is necessary.

The attack complexity is low, although Microsoft currently assesses successful exploitation as less likely.

Business Impact

This vulnerability poses a serious risk to organizations that rely on Microsoft Office applications for everyday business activities.

Excel documents are frequently exchanged between employees, customers, suppliers, and external partners, making malicious Office attachments a potential entry point for cyberattacks.

A single malicious document could turn a routine business task into a serious security incident.

Successful exploitation could result in several business consequences:

• Data Breaches: Attackers could gain unauthorized access to confidential documents, financial information, and sensitive business records.
• System Compromise: Malicious code execution could allow attackers to install malware or compromise affected systems.
• Operational Disruption: Compromised systems could become unavailable, affecting employee productivity and business continuity.
• Financial Losses: Security incidents could result in investigation costs, recovery expenses, and operational downtime.
• Reputational Damage: Unauthorized access to sensitive information could reduce customer confidence and damage business relationships.

Organizations with large numbers of Microsoft Office users may face increased exposure because employees regularly receive and open documents from external sources.

The biggest risk is not simply opening a malicious spreadsheet. It is what an attacker could do after successfully executing code.

Workaround

Microsoft has not identified any official mitigations or workarounds for this vulnerability.

If immediate patch deployment is not possible, organizations should consider these precautionary measures:

• Avoid opening unexpected or suspicious Office attachments.
• Verify Office documents received from unknown senders.
• Use email security controls to identify potentially malicious attachments.
• Restrict unnecessary access to untrusted Office documents.
• Prioritize security updates for affected Microsoft Office installations.

These precautions may reduce exposure but do not eliminate the underlying vulnerability.

Urgency

Critical – High Priority Patch Deployment Recommended

CVE-2026-100210 should be prioritized for patch deployment because it carries a Critical severity rating and a CVSS score of 8.8.

The vulnerability allows remote code execution, requires no existing attacker privileges, and has low attack complexity.

Although there are no confirmed reports of active exploitation and Microsoft considers exploitation less likely, the potential consequences remain significant.

A successful attack could expose sensitive business information, compromise employee workstations, and interrupt critical operations.

Organizations should prioritize updating affected Microsoft Office products, particularly systems frequently used to open documents received from external sources.

For Office Online Server, administrators should review and deploy security update KB5002928.

Delaying this patch leaves a critical weakness in one of the most widely used business applications. One convincing malicious document could be enough to trigger a serious security incident.