Deserialization in Microsoft 365 Apps
CVE-2026-21511
Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.
Vulnerability class: Insecure Deserialization
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.038 (89.5th percentile), scored .
Low probability of exploitation in the next 30 days, but still tracked. 90th percentile — 89.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.036 · newest: 0.038 · 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 Office Ltsc For Mac 2021 — versions 16.0.1
- Microsoft Office Ltsc For Mac 2024 — versions 16.0.0
- Microsoft Sharepoint Enterprise Server 2016 — versions 16.0.0
- Microsoft Sharepoint Server 2019 — versions 16.0.0
- Microsoft Sharepoint Server Subscription Edition — versions 16.0.0
Weakness classification (CWE)
References
- Microsoft Outlook Spoofing Vulnerability (vendor-advisory, patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-21511?
- CVE-2026-21511 is a high-severity vulnerability in Microsoft 365 Apps, classified under Deserialization of Untrusted Data. CVSS score: 7.5/10. Published 2026-02-10.
- How severe is CVE-2026-21511?
- High severity. CVSS v3 base score is 7.5 out of 10.