What is CVE-2026-81389?

CVE-2026-81389 is a high-severity vulnerability in Microsoft 365 Apps, classified under Heap-based Buffer Overflow. CVSS score: 7.0/10. Published 2026-09-08.

How severe is CVE-2026-81389?

High severity. CVSS v3 base score is 7.0 out of 10.

Buffer overflow in Microsoft 365 Apps

CVE-2026-81389

Heap-based buffer overflow in Microsoft Office Excel allows an unauthorized attacker to execute code locally.

Vulnerability class: Buffer Overflow

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

CVSS v3 metric

CVSS v3 base score 7.0 (High). Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (29.6th percentile), scored 2026-10-25.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 30th percentile — 29.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-122 — Heap-based Buffer Overflow

References

Microsoft Excel Remote Code Execution Vulnerability (vendor-advisory, Patch, patch, Vendor Advisory)

Frequently asked questions

What is CVE-2026-81389?: CVE-2026-81389 is a high-severity vulnerability in Microsoft 365 Apps, classified under Heap-based Buffer Overflow. CVSS score: 7.0/10. Published 2026-09-08.
How severe is CVE-2026-81389?: High severity. CVSS v3 base score is 7.0 out of 10.