# CVE-2026-55129: Microsoft Office heap overflow remote code execution

Source: https://junglewise.ai/threats/cve-2026-55129-microsoft-office-heap-overflow-remote-code-execution  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-14. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-55129 · 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 full system takeover or data theft. This typically requires a user to open a specially crafted malicious file.

Technologies: [Microsoft 365 Apps for Enterprise](https://junglewise.ai/threats/technologies/365-apps-for-enterprise), [Microsoft Office 2016](https://junglewise.ai/threats/technologies/office-2016), [Microsoft Office 2019](https://junglewise.ai/threats/technologies/office-2019), [Microsoft Office 365 for Mac](https://junglewise.ai/threats/technologies/office-365-for-mac), [Microsoft Office LTSC 2021](https://junglewise.ai/threats/technologies/office-ltsc-2021), [Microsoft Office LTSC 2024](https://junglewise.ai/threats/technologies/office-ltsc-2024). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-55129 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55129 being exploited in the wild.

**How severe is CVE-2026-55129?** 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; Microsoft Office 2016 16.0.0 to 16.0.5561.1000; Microsoft Office 2019 >= 19.0.0; Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215; and 2 more.

**Is there a fix for CVE-2026-55129?** 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-2026-55129 attacked?** It is attacked with local access, in a network appliance.

**Am I affected by CVE-2026-55129?** 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, including Office 2016, 2019, LTSC, and Microsoft 365 Apps. The vulnerability is triggered when the application improperly handles memory during the processing of a malicious file. While the attack vector is local, it requires user interaction (UI:R), such as opening a booby-trapped 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 platforms.

## Affected products

- Microsoft Microsoft 365 Apps for Enterprise >= 16.0.1
- Microsoft Microsoft Office 2016 16.0.0 to 16.0.5561.1000
- Microsoft Microsoft Office 2019 >= 19.0.0
- Microsoft Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215
- Microsoft Microsoft Office LTSC 2021 >= 16.0.1
- Microsoft Microsoft Office LTSC 2024 >= 16.0.0

## Timeline

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

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55129](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55129)

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- [Microsoft Office out-of-bounds read information disclosure](https://junglewise.ai/threats/cve-2026-56195-microsoft-office-out-of-bounds-read-information-disclosure)
- [Microsoft Office Out-of-bounds Read Information Disclosure](https://junglewise.ai/threats/cve-2026-56192-microsoft-office-out-of-bounds-read-information-disclosure)
- [Microsoft Office Excel heap buffer overflow](https://junglewise.ai/threats/cve-2026-56156-microsoft-office-excel-heap-buffer-overflow)
- [Microsoft Excel use of uninitialized resource code execution](https://junglewise.ai/threats/cve-2026-55949-microsoft-excel-use-of-uninitialized-resource-code-execution)