Key points
- Microsoft assigns a CVSS score of 8.8 to this high-severity vulnerability.
- The flaw affects multiple versions of Microsoft Office, including LTSC and 365 Apps.
- Attackers need no authentication to exploit this heap-based buffer overflow.
Microsoft has published an advisory for CVE-2026-100210, a remote code execution vulnerability in Excel. This high-severity issue allows unauthorised attackers to execute arbitrary code over a network.
The flaw stems from a heap-based buffer overflow within the application. According to the National Vulnerability Database, the weakness is classified under CWE-122. This memory corruption issue permits remote code execution by unauthorised actors.
Context and background
This vulnerability is part of Microsoft's regular security update cycle. The advisory lists specific version thresholds for various Office products. Security teams should review the affected software list to determine exposure within their environments.
Who is affected
Multiple Microsoft Office versions are impacted by this advisory. Affected products include Microsoft 365 Apps for Enterprise, Office 365 for Mac, and Office LTSC 2021 versions prior to build 16.0.14334.20974. Office LTSC 2024 is also vulnerable before build 16.0.17932.21056. Mac LTSC editions for 2021 and 2024 are affected until publication.
What happens next
Organisations should immediately inventory their Excel installations against the affected version list. Security teams must verify whether their environments run vulnerable builds. Until a patch is confirmed and deployed, users should treat unsolicited Excel files with extreme caution. Monitor for any official updates from Microsoft regarding mitigation strategies.
Why this attack works
Heap overflows occur when an application writes data beyond the boundaries of allocated memory. This technique allows attackers to corrupt adjacent memory structures, potentially overwriting control data like function pointers. In intrusion stages, this serves as an initial access vector, granting remote code execution. Teams usually check for strict memory safety practices and input validation to mitigate such risks.
What to do and how to stay safe: Microsoft
- Verify all installed Excel versions against the affected build numbers listed in the advisory.
- Restrict macro execution and disable automatic processing of untrusted Office files.
- Monitor network logs for unusual outbound connections from Excel processes.
- Ensure endpoint detection tools are configured to alert on suspicious memory activity.
Step-by-step guide: Patch Management Policy: How to Automate Fixes Without Breaking Systems
General security guidance from the Payload Report newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is the CVSS score for CVE-2026-100210?
The National Vulnerability Database rates the severity as 8.8, which is classified as high.
Can an attacker exploit this without logging in?
Yes, the advisory states that unauthorised attackers can execute code over a network.
Which Excel versions are vulnerable?
Versions prior to 16.0.14334.20974 for LTSC 2021 and 16.0.17932.21056 for LTSC 2024 are affected.
