What is CVE-2026-77898?

CVE-2026-77898 is a high-severity vulnerability in Microsoft 365 Apps, classified under Heap-based Buffer Overflow. CVSS score: 7.5/10. Published 2026-09-08.

How severe is CVE-2026-77898?

High severity. CVSS v3 base score is 7.5 out of 10.

Buffer overflow in Microsoft 365 Apps

CVE-2026-77898

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

Vulnerability class: Buffer Overflow

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

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (48.5th percentile), scored 2026-10-24.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 48.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Weakness classification (CWE)

CWE-122 — Heap-based Buffer Overflow

References

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

Frequently asked questions

What is CVE-2026-77898?: CVE-2026-77898 is a high-severity vulnerability in Microsoft 365 Apps, classified under Heap-based Buffer Overflow. CVSS score: 7.5/10. Published 2026-09-08.
How severe is CVE-2026-77898?: High severity. CVSS v3 base score is 7.5 out of 10.