# CVE-2026-77898: Microsoft Office heap-based buffer overflow

Source: https://junglewise.ai/threats/cve-2026-77898-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-2026-77898 · Severity: high · CVSS 7.5 · Published 2026-09-08

Microsoft Office, a widely-used productivity suite for creating documents, spreadsheets, and presentations, contains a heap-based buffer overflow vulnerability. An attacker can exploit this flaw by sending a specially crafted file over the network, potentially allowing them to execute arbitrary code on a user's computer without authorization. This could lead to data theft, system compromise, or further malware installation.

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

## Quick answers

**Is CVE-2026-77898 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77898 being exploited in the wild.

**How severe is CVE-2026-77898?** High severity, with a CVSS score of 7.5, published 8 September 2026.

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

**Is there a fix for CVE-2026-77898?** 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-2026-77898 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-77898?** 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 exists in Microsoft Office that allows remote code execution without authentication. The vulnerability is reachable over the network, likely triggered by processing a malicious document file. An attacker can craft a specially formatted Office document that triggers the overflow, enabling arbitrary code execution in the context of the user running Office. The attack does not require user interaction beyond opening the malicious file. Microsoft has issued patches to address this vulnerability.

## Affected products

- Microsoft Office

## Timeline

- 2026-09-08: disclosed

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-77898](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-77898)

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