# CVE-2026-78511: Microsoft Word heap-based buffer overflow

Source: https://junglewise.ai/threats/cve-2026-78511-microsoft-word-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-2026-78511 · Severity: high · CVSS 8.8 · Published 2026-09-08

Microsoft Word, a widely used word processing application, contains a heap-based buffer overflow vulnerability that allows attackers to execute arbitrary code on a victim's computer when the user opens a specially crafted document. This vulnerability can be exploited remotely without any user credentials, enabling attackers to take full control of affected systems and potentially steal sensitive data or install malware.

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

## Quick answers

**Is CVE-2026-78511 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-78511 being exploited in the wild.

**How severe is CVE-2026-78511?** High severity, with a CVSS score of 8.8, published 8 September 2026.

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

**Is there a fix for CVE-2026-78511?** 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-2026-78511 attacked?** It is attacked over the network.

**Am I affected by CVE-2026-78511?** Check whether you run Microsoft Word. 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

The vulnerability is a heap-based buffer overflow in Microsoft Word's document parsing logic. An attacker can craft a malicious Word document that triggers the overflow when processed, allowing arbitrary code execution with the privileges of the user running Word. The attack vector is network-based through document delivery, with the primary precondition being user interaction (opening the malicious file). No authentication is required. A patch is expected from Microsoft; consult the Microsoft Security Response Center for availability and guidance.

## Affected products

- Microsoft Word

## Timeline

- 2026-09-08: disclosed

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78511](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-78511)

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