CVE-2026-55131: Microsoft Excel heap buffer overflow code execution

CVE-2026-55131 · Severity: high · CVSS 7.8 · Published 2026-07-14

A vulnerability in Microsoft Excel could allow an attacker to execute malicious code on a user's computer. This typically occurs if a user is tricked into opening a specially crafted Excel file. Successful exploitation could lead to a full compromise of the user's data and local system access.

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-2026-55131 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55131 being exploited in the wild.
How severe is CVE-2026-55131?
High severity, with a CVSS score of 7.8, published 14 July 2026.
Which products and versions are affected?
Microsoft 365 Apps for Enterprise >= 16.0.1; Microsoft Excel 2016 16.0.0.0 to 16.0.5561.1001; Microsoft Office 2019 >= 19.0.0; Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215; and 3 more.
Is there a fix for CVE-2026-55131?
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-2026-55131 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55131?
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 heap-based buffer overflow (CWE-122) exists in Microsoft Excel across multiple versions, including Office 2016, 2019, 2021, and Microsoft 365 Apps. The vulnerability is triggered when the application processes a malformed file, leading to memory corruption. An attacker can exploit this by convincing a user to open a malicious spreadsheet, resulting in arbitrary code execution in the context of the current user. The attack vector is local with a requirement for user interaction (UI:R). Microsoft has released security updates to address this issue.

Affected products

  • Microsoft Microsoft 365 Apps for Enterprise >= 16.0.1
  • Microsoft Microsoft Excel 2016 16.0.0.0 to 16.0.5561.1001
  • Microsoft Microsoft Office 2019 >= 19.0.0
  • Microsoft Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215
  • Microsoft Microsoft Office LTSC 2021 >= 16.0.1
  • Microsoft Microsoft Office LTSC 2024 >= 16.0.0
  • Microsoft Office Online Server 16.0.0.0 to 16.0.10417.20175

Timeline

  • 2026-07-14: disclosed: Initial publication of the CVE record.
  • 2026-07-14: advisory: Microsoft released security update details.

References

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