CVE-2026-55056: Microsoft Office heap buffer overflow

CVE-2026-55056 · Severity: high · CVSS 7.8 · 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 run malicious code on a user's computer if the user is tricked into opening a specially crafted file. This could lead to a full system compromise, allowing the attacker to steal sensitive data, install malware, or disrupt business operations.

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-2026-55056 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55056 being exploited in the wild.
How severe is CVE-2026-55056?
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 up to latest security release; Microsoft Office 2016 16.0.0 to 16.0.5561.1000; Microsoft Office 2019 19.0.0 up 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-2026-55056?
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-2026-55056 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55056?
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 improperly handles memory while processing a specially crafted file. Although the attack vector is local, it requires no prior privileges (PR:N) but does require user interaction (UI:R), such as opening a malicious document. Successful exploitation allows for arbitrary code execution in the context of the current user. Microsoft has released security updates to address this issue across affected versions of Office 2016, 2019, LTSC, and Microsoft 365 Apps.

Affected products

  • Microsoft Microsoft 365 Apps for Enterprise 16.0.1 up to latest security release
  • Microsoft Microsoft Office 2016 16.0.0 to 16.0.5561.1000
  • Microsoft Microsoft Office 2019 19.0.0 up 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 up to latest security release
  • Microsoft Microsoft Office LTSC 2024 16.0.0 up 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: disclosed
  • 2026-07-14: advisory

References

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