CVE-2026-100211 – Microsoft Office Excel Remote Code Execution Vulnerability

Microsoft has identified a critical remote code execution (RCE) vulnerability in Microsoft Office Excel that could allow an unauthorized attacker to execute malicious code on an affected system. The vulnerability, tracked as CVE-2026-100211, results from a Use-After-Free (CWE-416) memory management flaw. An attacker could exploit this weakness by convincing a user to open a specially crafted Office file. Successful exploitation could compromise sensitive information, allow unauthorized system modifications, and disrupt business operations. The vulnerability has a CVSS score of 8.8 and is classified as Critical. Although exploitation is considered less likely, the potential consequences make timely patching important.

CVSS SCORE: 8.8

SEVERITY: Critical

Threat

This vulnerability presents a significant security risk because attackers could execute malicious code through a specially crafted Microsoft Office file.

An attacker does not need existing privileges on the targeted system. However, successful exploitation requires user interaction, specifically opening a malicious Office document.

The vulnerability has low attack complexity and could result in serious consequences, including:

• Unauthorized execution of malicious code.
• Theft or exposure of confidential business information.
• Installation of malware or other malicious software.
• Unauthorized modification of files and system data.
• Disruption of business operations and system availability.

The Preview Pane is not an attack vector for this vulnerability.

Exploits

Microsoft has classified this vulnerability as Exploitation Less Likely.

The vulnerability has not been publicly disclosed, and there are no reported instances of active exploitation.

Exploit code maturity is classified as Unproven, meaning the existence of publicly available working exploit code has not been confirmed.

There is also no confirmed evidence of publicly available proof-of-concept (PoC) exploit code or zero-day exploitation.

Despite the absence of reported exploitation, attackers could potentially develop malicious Office documents designed to trigger the vulnerability.

Technical Summary

CVE-2026-100211 is a Use-After-Free (CWE-416) vulnerability affecting Microsoft Office Excel.

A Use-After-Free vulnerability occurs when an application attempts to access memory after that memory has already been released. This can create unsafe memory conditions that attackers may exploit to manipulate application behavior or execute malicious instructions.

In this case, the vulnerability could allow an unauthorized attacker to achieve remote code execution through a specially crafted Microsoft Office file.

The attack process involves delivering a malicious Office document to a targeted user and convincing them to open it.

When the vulnerable application processes the malicious file, the memory management weakness could potentially be triggered, allowing attacker-controlled code to execute.

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 attackers to have existing privileges on the affected system, making malicious document delivery a potential attack method.

However, exploitation depends on convincing a user to open the malicious document.

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

Exploitability

The vulnerability affects the following Microsoft Office products:

• Microsoft 365 Apps for Enterprise (32-bit systems)
• Microsoft 365 Apps for Enterprise (64-bit systems)
• Microsoft Office LTSC 2024 (32-bit editions)
• Microsoft Office LTSC 2024 (64-bit editions)

Attackers could attempt exploitation by distributing malicious Office files through phishing emails or other document-sharing methods.

The attacker must convince the recipient to open the malicious file.

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

Microsoft assesses exploitation as less likely.

Specific vulnerable build numbers and fixed build versions are not confirmed.

Business Impact

This vulnerability represents a serious security concern for organizations that rely on Microsoft Excel and Microsoft 365 applications for daily business activities.

“A trusted business document can become an attacker’s entry point. One malicious spreadsheet could threaten sensitive information, system integrity, and business continuity.”

If successfully exploited, attackers could execute malicious code on affected systems, potentially compromising corporate information and disrupting normal operations.

The potential business consequences include:

• Sensitive Data Exposure: Attackers could gain unauthorized access to confidential business information, financial documents, or other sensitive data accessible on the compromised system.
• Malware Infection: Successful remote code execution could allow attackers to install malicious software or establish additional malicious activity.
• Operational Disruption: Compromised systems could experience application failures, unauthorized changes, or interruptions to important business processes.
• Financial Losses: Security incidents involving compromised endpoints could result in investigation expenses, recovery costs, and operational downtime.
• Reputational Damage: Exposure of sensitive information or disruption of critical business services could damage customer confidence and organizational reputation.

Organizations that frequently exchange Excel documents with external parties may face additional exposure to malicious document-based attacks.

Workaround

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

Until the security update can be deployed, organizations should consider these general precautions:

• Avoid opening unexpected or suspicious Office attachments.
• Strengthen email security controls to detect malicious documents.
• Educate employees about phishing and malicious Office files.
• Use endpoint protection to monitor suspicious application behavior.
• Prioritize deployment of the official Microsoft security update.

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

Urgency

Critical – Prioritize Security Update Deployment

CVE-2026-100211 should be prioritized for remediation because it carries a Critical severity rating and a CVSS score of 8.8.

The vulnerability could allow remote code execution without requiring attackers to possess existing system privileges.

Although Microsoft currently considers exploitation less likely, the vulnerability’s low attack complexity and potential for significant confidentiality, integrity, and availability impacts make it a serious concern.

Organizations should prioritize updating affected Microsoft 365 Apps for Enterprise and Microsoft Office LTSC 2024 installations.

Security teams should also reinforce awareness of malicious Office documents and monitor endpoints for suspicious activity.

The absence of known attacks does not eliminate the risk. Deploying the security update before exploitation occurs is the strongest defense.