CVE-2026-78505: Microsoft Office Remote Code Execution Vulnerability

Overview

Severity
High (CVSS 8.8)
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Category
Remote Code Execution
Exploit Status
Not Exploited
Exploitation Likelihood
Less Likely
Patch Tuesday
2026-Sep
Released
2026-09-08

Description

Heap-based buffer overflow in Microsoft Office allows an unauthorized attacker to execute code over a network.

FAQ

Are the updates for the Microsoft Office LTSC for Mac currently available? The security update for Microsoft Office LTSC for Mac 2021 and 2024 are not immediately available. The updates will be released as soon as possible, and when they are available, customers will be notified via a revision to this CVE information. Is the Preview Pane an attack vector for this vulnerability? Yes, the Preview Pane is an attack vector. How could an attacker exploit this vulnerability? An attacker could convince a user to open and save a specially crafted Microsoft Office document. Successful exploitation could allow the attacker to execute code in the context of the user. Authentication is not required, but user interaction is required.

Affected Products (13)

Microsoft Office

  • Microsoft Office 365 for Mac
  • Microsoft Office 2019 for 32-bit editions
  • Microsoft Office 2019 for 64-bit editions
  • Microsoft 365 Apps for Enterprise for 32-bit Systems
  • Microsoft 365 Apps for Enterprise for 64-bit Systems
  • Microsoft Office LTSC for Mac 2021
  • Microsoft Office LTSC 2021 for 64-bit editions
  • Microsoft Office LTSC 2021 for 32-bit editions
  • Microsoft Office LTSC 2024 for 32-bit editions
  • Microsoft Office LTSC 2024 for 64-bit editions
  • Microsoft Office LTSC for Mac 2024
  • Microsoft Office 2016 (32-bit edition)
  • Microsoft Office 2016 (64-bit edition)

Security Updates (1)

Acknowledgments

Kentaro Kawane with GMO Cybersecurity by Ierae, Inc., <a href="https://x.com/lmksecurity">Jeongmin Choi</a>, <a href="https://x.com/seadragnol">SeaDragnoL</a> with <a href="https://x.com/qriousec">Qrious Secure</a>

Revision History

  • 2026-09-08: Information published.