CVE-2026-55029: Microsoft Excel heap buffer overflow in file parsing

CVE-2026-55029 · 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 software installation, 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-2026-55029 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55029 being exploited in the wild.
How severe is CVE-2026-55029?
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 to latest security release; Microsoft Excel 2016 16.0.0.0 to 16.0.5561.1001; Microsoft Office 2019 19.0.0 to latest security release; Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215; and 3 more.
Is there a fix for CVE-2026-55029?
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-2026-55029 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55029?
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 due to improper validation of user-supplied data when parsing spreadsheet files. The vulnerability is triggered when a user opens a maliciously crafted Excel file. Although the attack vector is local, it requires no prior privileges (PR:N) but does require user interaction (UI:R). Successful exploitation allows an attacker to execute arbitrary code in the context of the current user, potentially leading to full system compromise. Microsoft has released security updates to address this issue across various versions of Office and Excel.

Affected products

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

Timeline

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

References

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