# CVE-2026-78505: Microsoft Office heap-based buffer overflow

Source: https://junglewise.ai/threats/cve-2026-78505-microsoft-office-heap-based-buffer-overflow  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-08. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-78505 · Severity: high · CVSS 8.8 · Published 2026-09-08

Microsoft Office is a suite of productivity applications used across enterprises to create and edit documents, spreadsheets, and presentations. A heap-based buffer overflow vulnerability in Office could allow an attacker to execute arbitrary code on an affected system simply by sending a specially crafted file over the network, potentially leading to data theft, system compromise, or lateral movement through an organization.

Technologies: [Microsoft Office](https://junglewise.ai/threats/technologies/office). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-78505 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-78505 being exploited in the wild.

**How severe is CVE-2026-78505?** High severity, with a CVSS score of 8.8, published 8 September 2026.

**Which products and versions are affected?** Microsoft Office.

**Is there a fix for CVE-2026-78505?** 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-2026-78505 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-78505?** Check whether you run Microsoft Office. 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 exists in Microsoft Office that does not properly validate buffer boundaries during memory operations. The vulnerability can be triggered remotely when a user opens or processes a malicious Office document, without requiring authentication. An attacker can craft a specially formatted file that, when processed by Office, overflows a heap buffer and overwrites adjacent memory, achieving code execution with the privileges of the user running Office. A patch is expected from Microsoft through their regular security update cycle.

## Affected products

- Microsoft Office

## Timeline

- 2026-09-08: disclosed

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78505](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78505)

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