Out-of-bounds Read in Microsoft 365 Apps
CVE-2026-63521
Out-of-bounds read in Microsoft Office Word allows an unauthorized attacker to disclose information locally.
Vulnerability class: Buffer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.5 (Medium). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.004 (35.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 35.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.001
Affected products
- Microsoft 365 Apps
- Microsoft 365 Apps For Enterprise — versions 16.0.1
- Microsoft Office 2019 — versions 19.0.0
- Microsoft Office Ltsc 2021 — versions 16.0.1
- Microsoft Office Ltsc 2024 — versions 16.0.0
- Microsoft Word 2016 — versions 16.0.1
- Microsoft Office 2019
- Microsoft Office 2021
- Microsoft Office 2024
- Microsoft Word — versions 2016
Weakness classification (CWE)
References
- Microsoft Office Word Information Disclosure Vulnerability (vendor-advisory, Patch, patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-63521?
- CVE-2026-63521 is a medium-severity vulnerability in Microsoft 365 Apps, classified under Out-of-bounds Read. CVSS score: 5.5/10. Published 2026-08-11.
- How severe is CVE-2026-63521?
- Medium severity. CVSS v3 base score is 5.5 out of 10.