CVE-2026-78515: Microsoft Office Excel Information Disclosure Vulnerability

Overview

Severity: Medium (CVSS 6.5)
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C
Category: Information Disclosure
Exploit Status: Not Exploited
Exploitation Likelihood: Less Likely
Patch Tuesday: 2026-Sep
Released: 2026-09-08

Description

Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to disclose information over a network.

FAQ

Is the Preview Pane an attack vector for this vulnerability? Yes, the Preview Pane is an attack vector. What type of information could be disclosed by this vulnerability? An attacker who successfully exploited this vulnerability could potentially read small portions of heap memory. 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.

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 (2)

Acknowledgments

<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>, <a href="https://x.com/gr4ss341">grass</a> with <a href="https://x.com/vcslab">Viettel Cyber Security</a>

Revision History

2026-09-08: Information published.