CVE-2026-55121: Microsoft Office out-of-bounds read information disclosure

CVE-2026-55121 · Severity: medium · CVSS 5.5 · Published 2026-07-14

A security vulnerability exists in Microsoft Office, the widely used suite of productivity applications including Word, Excel, and PowerPoint. An attacker could exploit this flaw to gain unauthorized access to information stored on a user's local computer. To be successful, an attacker would typically need to trick a user into opening a specially crafted file.

Technologies: Microsoft 365 Apps for Enterprise, Microsoft Office 2016, Microsoft Office 2019, Microsoft Office 365 for Mac, Microsoft Office LTSC 2021, Microsoft Office LTSC 2024, Microsoft SharePoint Enterprise Server 2016. Vendors: Microsoft.

Quick answers

Is CVE-2026-55121 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55121 being exploited in the wild.
How severe is CVE-2026-55121?
Medium severity, with a CVSS score of 5.5, published 14 July 2026.
Which products and versions are affected?
Microsoft 365 Apps for Enterprise All versions prior to July 2024 updates; Microsoft Office 2016 versions prior to 16.0.5561.1000; Microsoft Office 2019 All versions prior to July 2024 updates; Microsoft Office 365 for Mac versions prior to 16.111.26071215; and 3 more.
Is there a fix for CVE-2026-55121?
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-2026-55121 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55121?
Check whether you run Microsoft 365 Apps for Enterprise, Microsoft Office 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

An out-of-bounds read vulnerability (CWE-125) exists in multiple versions of Microsoft Office and SharePoint Server. The flaw is triggered when the application improperly handles memory while parsing a specially crafted file. An attacker can exploit this by convincing a user to open a malicious document, leading to the disclosure of sensitive information from the process memory. The attack is local in nature and requires user interaction. Microsoft has released security updates to address this issue across affected platforms including Windows and macOS.

Affected products

  • Microsoft Microsoft 365 Apps for Enterprise All versions prior to July 2024 updates
  • Microsoft Microsoft Office 2016 versions prior to 16.0.5561.1000
  • Microsoft Microsoft Office 2019 All versions prior to July 2024 updates
  • Microsoft Microsoft Office 365 for Mac versions prior to 16.111.26071215
  • Microsoft Microsoft Office LTSC 2021 All versions prior to July 2024 updates
  • Microsoft Microsoft Office LTSC 2024 All versions prior to July 2024 updates
  • Microsoft Microsoft SharePoint Enterprise Server 2016 versions prior to 16.0.5561.1001

Timeline

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

References

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