# CVE-2026-55947: Microsoft Office Excel heap buffer overflow

Source: https://junglewise.ai/threats/cve-2026-55947-microsoft-office-excel-heap-buffer-overflow  
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-2026-55947 · Severity: high · CVSS 7.8 · Published 2026-07-14

A security vulnerability exists in Microsoft Excel, the widely used spreadsheet application. An attacker could exploit this flaw by tricking a user into opening a specially crafted file, potentially allowing the attacker to take control of the user's computer. This could lead to the theft of sensitive data, installation of malicious software, or disruption of business operations.

Technologies: [Microsoft 365 Apps for Enterprise](https://junglewise.ai/threats/technologies/365-apps-for-enterprise), [Microsoft Excel 2016](https://junglewise.ai/threats/technologies/excel-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), [Microsoft Office Online Server](https://junglewise.ai/threats/technologies/office-online-server). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-55947 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55947 being exploited in the wild.

**How severe is CVE-2026-55947?** 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 Excel 2016 16.0.0.0 to 16.0.5561.1001; Microsoft Office 2019 >= 19.0.0; Microsoft Office 365 for Mac 1.0.0 to 16.111.26071215; and 3 more.

**Is there a fix for CVE-2026-55947?** 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-2026-55947 attacked?** It is attacked with local access, in a network appliance.

**Am I affected by CVE-2026-55947?** Check whether you run Microsoft 365 Apps for Enterprise, Microsoft Excel 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 vulnerability (CWE-122) exists in Microsoft Office Excel. The flaw is triggered when the application improperly handles objects in memory while processing a specially crafted file. An attacker can exploit this by convincing a user to open a malicious Excel document, leading to arbitrary code execution in the context of the current user. The attack vector is local, requiring user interaction (UI:R), and affects multiple versions of Office across Windows and macOS, as well as Office Online Server. Microsoft has released security updates to address this issue.

## Affected products

- Microsoft Microsoft 365 Apps for Enterprise >= 16.0.1
- Microsoft Microsoft Excel 2016 16.0.0.0 to 16.0.5561.1001
- 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
- Microsoft Office Online Server 16.0.0.0 to 16.0.10417.20175

## Timeline

- 2026-07-14: disclosed: Initial publication of the CVE record.
- 2026-07-14: advisory: Microsoft released security update details.

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55947](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55947)

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