What is CVE-2026-78518?

CVE-2026-78518 is a high-severity vulnerability in Microsoft 365 Apps, classified under Improper Input Validation. CVSS score: 8.8/10. Published 2026-09-08.

How severe is CVE-2026-78518?

High severity. CVSS v3 base score is 8.8 out of 10.

Out-of-bounds Read in Microsoft 365 Apps

CVE-2026-78518

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

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

CVSS v3 metric

CVSS v3 base score 8.8 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

Affected products

Microsoft 365_apps
Microsoft Excel — versions 2016
Microsoft Microsoft_365
Microsoft 365 Apps For Enterprise
Microsoft Excel 2016
Microsoft Office 2016
Microsoft Office 2019
Microsoft Office 365 For Mac
Microsoft Office Ltsc 2021
Microsoft Office Ltsc 2024

Weakness classification (CWE)

CWE-20 — Improper Input Validation
CWE-125 — Out-of-bounds Read

References

secure@microsoft.com (vendor-advisory, Patch, patch, Vendor Advisory)

Frequently asked questions

What is CVE-2026-78518?: CVE-2026-78518 is a high-severity vulnerability in Microsoft 365 Apps, classified under Improper Input Validation. CVSS score: 8.8/10. Published 2026-09-08.
How severe is CVE-2026-78518?: High severity. CVSS v3 base score is 8.8 out of 10.