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)

Published 2026-09-08 · last modified 2026-09-17.

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.

EPSS exploit prediction

EPSS: 0.009 (58.1th percentile), scored 2026-10-24.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 58th percentile — 58.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Weakness classification (CWE)

References

Microsoft Office Excel Remote Code Execution Vulnerability (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.