CVE-2026-55137: Microsoft Office Excel heap buffer overflow

CVE-2026-55137 · Severity: high · CVSS 7.8 · Published 2026-07-14

A security vulnerability exists in Microsoft Excel, the widely used spreadsheet application. An attacker could exploit this flaw by tricking a user into opening a specially crafted file, potentially allowing the attacker to take control of the user's computer. This could lead to the theft of sensitive data, unauthorized changes to files, or a complete system compromise.

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 LTSC for Mac 2021, Microsoft Office LTSC for Mac 2024, Microsoft Office Online Server. Vendors: Microsoft.

Quick answers

Is CVE-2026-55137 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55137 being exploited in the wild.
How severe is CVE-2026-55137?
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 and later; Microsoft Excel 2016 16.0.0.0 to 16.0.5561.1001; Microsoft Office 2019 19.0.0 and later; Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215; and 5 more.
Is there a fix for CVE-2026-55137?
A patch was published on 2026-07-14: Security updates made available via Microsoft Update Guide Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55137 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55137?
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 Office Excel across multiple versions, including Office 2016, 2019, 2021, 2024, and Microsoft 365 Apps. The vulnerability is triggered when the application fails to properly validate input while processing a specially crafted Excel file. An attacker can exploit this by convincing a user to open a malicious document, leading to arbitrary code execution in the context of the current user. The attack vector is local, but requires user interaction (UI:R). Microsoft has released security updates to address this issue.

Affected products

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

Timeline

  • 2026-07-14: advisory: Initial disclosure by Microsoft and NVD
  • 2026-07-14: patched: Security updates made available via Microsoft Update Guide

References

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