CVE-2026-55058: Microsoft Excel out-of-bounds read code execution

CVE-2026-55058 · Severity: high · CVSS 7.8 · Published 2026-07-14

Microsoft Excel, a widely used spreadsheet application, contains a security vulnerability that could allow an attacker to take control of a user's computer. To exploit this, an attacker would typically need to trick a user into opening a specially crafted malicious Excel file. If successful, the attacker could run unauthorized programs, access sensitive data, or disrupt business operations on the affected machine.

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-2026-55058 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55058 being exploited in the wild.
How severe is CVE-2026-55058?
High severity, with a CVSS score of 7.8, published 14 July 2026.
Which products and versions are affected?
Microsoft 365 Apps for Enterprise versions before July 2024 update; Microsoft Excel 2016 versions before 16.0.5561.1001; Microsoft Office 2019 versions before July 2024 update; Microsoft Office 365 for Mac versions before 16.111.26071215; and 3 more.
Is there a fix for CVE-2026-55058?
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-2026-55058 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55058?
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 multiple versions of Microsoft Excel and Office suites. The flaw is triggered when the application fails to properly validate input while reading data from a file, leading to memory corruption. An attacker can exploit this by convincing a user to open a maliciously crafted Excel document. Successful exploitation grants the attacker the ability to execute arbitrary code in the context of the current user. Affected products include Excel 2016, Office 2019, Office LTSC 2021/2024, and Microsoft 365 Apps across Windows and Mac platforms. Microsoft has released security updates to address this issue.

Affected products

  • Microsoft Excel 2016 versions before 16.0.5561.1001
  • Microsoft Office 2019 versions before July 2024 update
  • Microsoft Office LTSC 2021 versions before July 2024 update
  • Microsoft Office LTSC 2024 versions before July 2024 update
  • Microsoft 365 Apps for Enterprise versions before July 2024 update
  • Microsoft Office 365 for Mac versions before 16.111.26071215
  • Microsoft Office Online Server versions before 16.0.10417.20175

Timeline

  • 2026-07-14: disclosed
  • 2026-07-14: advisory: Microsoft released security updates for affected products.

References

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