CVE-2026-55140: Microsoft Office heap buffer overflow

CVE-2026-55140 · Severity: high · CVSS 7.8 · Published 2026-07-14

A security vulnerability has been identified in Microsoft Office, the widely used suite of productivity applications. An attacker could exploit this flaw to run unauthorized code on a user's computer, potentially leading to data theft or full system compromise. To be successful, the attacker must convince a user to open 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 Office LTSC for Mac 2021, Microsoft Office LTSC for Mac 2024. Vendors: Microsoft.

Quick answers

Is CVE-2026-55140 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55140 being exploited in the wild.
How severe is CVE-2026-55140?
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 Office 2016 16.0.0 to 16.0.5561.1000; Microsoft Office 2019 19.0.0 to latest security release; Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215; and 4 more.
Is there a fix for CVE-2026-55140?
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-2026-55140 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55140?
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

A heap-based buffer overflow (CWE-122) exists in multiple versions of Microsoft Office across Windows and macOS platforms. The vulnerability is triggered when the application fails to properly validate input while processing a malicious file, leading to memory corruption. An attacker can exploit this by convincing a user to open a specially crafted document, resulting in arbitrary code execution in the context of the current user. The attack vector is local, but requires user interaction (UI:R). Microsoft has released security updates to address this issue across affected versions including Office 2016, 2019, LTSC, and Microsoft 365 Apps.

Affected products

  • Microsoft Microsoft 365 Apps for Enterprise 16.0.1 to latest security release
  • Microsoft Microsoft Office 2016 16.0.0 to 16.0.5561.1000
  • 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 Microsoft Office LTSC for Mac 2021 16.0.1 to 16.111.26071215
  • Microsoft Microsoft Office LTSC for Mac 2024 16.0.0 to 16.111.26071215

Timeline

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

References

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