CVE-2026-55133: Microsoft Office OneNote heap overflow code execution

CVE-2026-55133 · Severity: high · CVSS 7.8 · Published 2026-07-14

Microsoft OneNote, a popular digital note-taking application, is vulnerable to a security flaw 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 file. If successful, the attacker could run malicious software, access sensitive data, or disrupt business operations on the affected device.

Technologies: Microsoft 365 Apps for Enterprise, Microsoft Office 365 for Mac, Microsoft Office LTSC for Mac 2021, Microsoft Office LTSC for Mac 2024. Vendors: Microsoft.

Quick answers

Is CVE-2026-55133 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55133 being exploited in the wild.
How severe is CVE-2026-55133?
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 versions prior to security release; Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215; Microsoft Office LTSC for Mac 2021 16.0.1 to 16.111.26071215; Microsoft Office LTSC for Mac 2024 16.0.0 to 16.111.26071215.
Is there a fix for CVE-2026-55133?
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-2026-55133 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55133?
Check whether you run Microsoft 365 Apps for Enterprise, Microsoft Office 365 for Mac, Microsoft Office LTSC for Mac 2021 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 vulnerability (CWE-122) exists in Microsoft Office OneNote. The vulnerability is triggered when the application improperly handles memory allocation while processing a malicious file. An attacker can exploit this by convincing a user to open a specially crafted document, leading to arbitrary code execution in the context of the current user. The attack vector is local, requiring user interaction (UI:R), but does not require prior administrative privileges (PR:N). Microsoft has released security updates to address this issue across affected versions of Office 365 and LTSC for both Windows and Mac.

Affected products

  • Microsoft 365 Apps for Enterprise 16.0.1 and later versions prior to security release
  • Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215
  • Microsoft Office LTSC for Mac 2021 16.0.1 to 16.111.26071215
  • Microsoft Office LTSC for Mac 2024 16.0.0 to 16.111.26071215

Timeline

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

References

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