CVE-2026-100210 in Excel
Summary
by MITRE • 10/13/2026
Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/13/2026
The vulnerability described constitutes a critical security flaw within the Microsoft Office Excel application, specifically manifesting as a heap-based buffer overflow. This type of memory corruption error occurs when a program writes data beyond the allocated boundaries of a buffer located in the heap segment of computer memory. In the context of Excel, this typically involves the processing of complex or malformed spreadsheet files that contain specially crafted objects, formulas, or embedded elements designed to exploit specific parsing routines within the application's engine. When an attacker crafts a malicious document with precise data structures, they can trigger an overflow condition where excess data overwrites adjacent memory locations on the heap. This corruption disrupts the normal flow of execution and allows for arbitrary code injection, effectively granting the attacker control over the affected system.
The operational impact of this vulnerability is severe due to its potential for remote code execution via a network vector. Since Microsoft Office Excel is widely used in enterprise environments for data analysis and reporting, it serves as an attractive target for threat actors. An unauthorized attacker does not necessarily need physical access or user credentials if the vulnerability can be triggered through file sharing mechanisms, email attachments, or web-based document storage services that automatically render previews of files. By convincing a victim to open a malicious Excel file, either directly or indirectly through automated preview features in operating systems like Windows Explorer, the attacker can execute arbitrary code with the privileges of the current user. This often leads to full system compromise, allowing for data exfiltration, installation of malware such as ransomware or backdoors, and lateral movement within the corporate network.
From a technical classification perspective, this vulnerability aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-120 Buffer Overflow without NULL Termination or more broadly CWE-787 Out-of-bounds Write in the heap space. The exploitation technique is consistent with ATT&CK tactics involving Initial Access and Execution, specifically leveraging techniques like Spearphishing Attachment where malicious files are used to deliver exploits. The lack of proper bounds checking during memory allocation and data copying operations represents a fundamental failure in secure coding practices within the application's legacy codebase or specific add-in modules. Such flaws often persist due to backward compatibility requirements with older file formats, which may utilize parsing logic that is less rigorous than modern standards for input validation and memory management.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary defense involves applying the latest security patches released by Microsoft through Windows Update or the Office update channel, as these updates typically include fixes for heap overflow conditions by implementing stricter bounds checking and safer memory handling routines. Organizations should enforce strict email filtering policies to block executable content and restrict macro-enabled files from untrusted sources. Additionally, enabling Protected View in Excel ensures that documents opened from potentially unsafe locations are loaded in a sandboxed environment with limited permissions, preventing active code execution until the user explicitly trusts the file. Network segmentation can also limit the blast radius of an infection by restricting lateral movement between systems where Office applications are deployed and critical infrastructure components.