CVE-2026-55031: Microsoft Excel out-of-bounds read code execution

CVE-2026-55031 · Severity: high · CVSS 7.8 · Published 2026-07-14

Microsoft Excel is a widely used spreadsheet application for data analysis and reporting. A security vulnerability has been identified that could allow an attacker to take control of a user's computer if the user is tricked into opening a specially crafted Excel file. This could lead to the theft of sensitive data, installation of malware, or disruption of business operations.

Technologies: Microsoft 365 Apps for Enterprise, Microsoft Excel 2016, Microsoft Office 2019, Microsoft Office 365 for Mac, Microsoft Office LTSC 2021, Microsoft Office LTSC 2024, Microsoft Office Online Server. Vendors: Microsoft.

Quick answers

Is CVE-2026-55031 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55031 being exploited in the wild.
How severe is CVE-2026-55031?
High severity, with a CVSS score of 7.8, published 14 July 2026.
Which products and versions are affected?
Microsoft 365 Apps for Enterprise All versions prior to July 2026 update; Microsoft Excel 2016 < 16.0.5561.1001; Microsoft Office 2019 All versions prior to July 2026 update; Microsoft Office 365 for Mac < 16.111.26071215; and 3 more.
Is there a fix for CVE-2026-55031?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-55031 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55031?
Check whether you run Microsoft 365 Apps for Enterprise, Microsoft Excel 2016, Microsoft Office 2019 or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A vulnerability classified as an out-of-bounds read (CWE-125) exists in Microsoft Excel. The flaw is triggered when the application fails to properly validate memory boundaries while parsing a maliciously crafted spreadsheet file. An attacker can exploit this by convincing a user to open a compromised file, leading to arbitrary code execution in the context of the current user. The attack vector is local, requiring user interaction (UI:R), and affects multiple versions of Office across Windows and macOS, as well as Office Online Server. Microsoft has released security updates to address this issue.

Affected products

  • Microsoft Microsoft Excel 2016 < 16.0.5561.1001
  • Microsoft Microsoft 365 Apps for Enterprise All versions prior to July 2026 update
  • Microsoft Microsoft Office 2019 All versions prior to July 2026 update
  • Microsoft Microsoft Office LTSC 2021 All versions prior to July 2026 update
  • Microsoft Microsoft Office LTSC 2024 All versions prior to July 2026 update
  • Microsoft Microsoft Office 365 for Mac < 16.111.26071215
  • Microsoft Office Online Server < 16.0.10417.20175

Timeline

  • 2026-07-14: disclosed
  • 2026-07-14: advisory

References

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