CVE-2026-55054: Microsoft Excel out-of-bounds read information disclosure

CVE-2026-55054 · Severity: medium · CVSS 6.5 · Published 2026-07-14

Microsoft Excel, a widely used spreadsheet application, contains a security vulnerability that could allow an attacker to access sensitive information. To exploit this, an attacker would typically need to trick a user into opening a specially crafted file. Successful exploitation could lead to the unauthorized disclosure of data from the user's system or memory.

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-2026-55054 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55054 being exploited in the wild.
How severe is CVE-2026-55054?
Medium severity, with a CVSS score of 6.5, published 14 July 2026.
Which products and versions are affected?
Microsoft 365 Apps for Enterprise versions prior to July 2026 updates; Microsoft Excel 2016 < 16.0.5561.1001; Microsoft Office 2019 versions prior to July 2026 updates; Microsoft Office 365 for Mac < 16.111.26071215; and 5 more.
Is there a fix for CVE-2026-55054?
A patch was published on 2026-07-14: Security updates made available via Microsoft Security Update Guide. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55054 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-55054?
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

This vulnerability is classified as an out-of-bounds read (CWE-125) within Microsoft Excel. The flaw occurs when the application processes a specially crafted file, leading to memory access outside of the intended buffer. An attacker can exploit this by hosting a malicious file and convincing a user to open it (User Interaction required). Successful exploitation allows the attacker to read sensitive information from the process memory, which could be used to bypass security mitigations or facilitate further attacks. Microsoft has released security updates to address this issue across affected Office versions.

Affected products

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

Timeline

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

References

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