Patch Excel Now: Microsoft Fixes High-Severity Remote Code Execution Flaw

Microsoft has released security updates to fix a serious flaw in Microsoft Office Excel that allows attackers to take control of a computer remotely. This vulnerability, tracked as CVE-2026-100210, has been rated with a CVSS score of 8.8, which classifies it as high severity. System administrators should prioritize installing these patches immediately to protect their environments from potential exploitation.

In plain English

The core issue is a heap-based buffer overflow within the Excel application. In simple terms, this means the program does not properly manage the memory space it uses while running. When Excel processes certain data, it can write more information than the allocated memory space can hold. This overflow can corrupt adjacent memory areas, allowing an attacker to inject and run malicious code on the host machine without needing prior access or authentication.

The background

This vulnerability affects several versions of Microsoft Office. According to the National Vulnerability Database, Microsoft 365 Apps for Enterprise versions prior to the latest security release are affected. Microsoft Office 365 for Mac versions before the upcoming publication date are also vulnerable. Additionally, Microsoft Office LTSC 2021 versions before build 16.0.14334.20974 and Microsoft Office LTSC 2024 versions before build 16.0.17932.21056 are at risk. Mac versions of LTSC 2021 and 2024 are affected until their respective publications.

This incident follows a pattern of Microsoft addressing remote execution flaws in its core productivity suite. As Vector Update reported on 2026-10-14, Microsoft recently patched a high-severity integer overflow in .NET Desktop Runtime that allowed remote privilege escalation. On the same date, the outlet noted that Microsoft released a fix for an unauthenticated remote code execution flaw in the Windows DHCP Server. These consecutive updates highlight the ongoing need for rigorous patch management across Microsoft platforms.

What changes now

Organizations must verify their current Excel versions against the affected lists provided by Microsoft. Users of Microsoft 365 should ensure their applications are set to update automatically or manually trigger the latest security release. For LTSC users, administrators need to manually install the specific builds mentioned in the advisory. Failure to update leaves systems exposed to network-based attacks where an attacker can send a specially crafted file to trigger the overflow and gain control of the system.

Key terms explained

A heap-based buffer overflow occurs when a program writes data beyond the boundaries of its allocated memory block in the heap area. This can overwrite critical data structures or execution pointers, potentially allowing an attacker to hijack the program's flow. Teams usually monitor for unusual memory usage or application crashes as early indicators. Check whether your endpoint detection tools are configured to alert on suspicious process injections or unexpected code execution attempts within office applications, as these behaviors often signal an active exploitation attempt.

Background: Privilege escalation attacks

Privilege escalation is the act of exploiting a bug, design flaw, or configuration oversight to gain elevated access to applications or data. Attackers use these techniques to move from a limited user account to an administrator or root level, allowing them to install malware, steal data, or persist within your environment.

Read the full guide: Privilege Escalation Attacks: How Attackers Steal Control

What to do and how to stay safe: Microsoft

• Verify that all workstations running Microsoft 365 or Office LTSC have installed the latest security updates provided by Microsoft.
• Restrict the ability to open or execute files from untrusted external sources to reduce the risk of triggering the vulnerability.
• Monitor network traffic and system logs for unusual activity from Excel processes, such as unexpected outbound connections or new process creations.
• Ensure that your endpoint protection solutions are updated to detect known indicators of compromise associated with Excel-based attacks.

Step-by-step guide: Risk-Based Vulnerability Management: Benefits, Limits, and Reality

General security guidance from the Vector Update newsroom. It is not confirmed advice from the organisations named in this story.

Frequently asked questions

Is this vulnerability being actively exploited in the wild?

The source material does not state whether this vulnerability is currently being exploited in the wild.

Do I need to patch my Mac version of Office?

Yes, Microsoft Office 365 for Mac and Office LTSC for Mac 2021 and 2024 are affected until their respective updates are published.

What is the CVSS score for this vulnerability?

The CVSS score for CVE-2026-100210 is 8.8, which is classified as high severity.