CVE-2026-21511

Microsoft Outlook Spoofing Vulnerability

CVE-2026-21511 is fixed in 5 products on 1 platform, first by KB5002840, released February 10, 2026. It is not reported as exploited, but the vendor rates exploitation more likely. Patch Radar priority: Urgent.

Urgent

CVSS

7.5

Important

Exploitation

More likely

Vendor assessment

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0397

90th percentile

<p>Deserialization of untrusted data in Microsoft Office Outlook allows an unauthorized attacker to perform spoofing over a network.</p>

Where it's fixed

Product	Fix	Released
Microsoft
Microsoft SharePoint Enterprise Server 2016	KB5002840	Feb 10, 2026
Microsoft SharePoint Enterprise Server 2016	KB5002841	Feb 10, 2026
Microsoft SharePoint Server 2019	KB5002836	Feb 10, 2026
Microsoft SharePoint Server 2019	KB5002834	Feb 10, 2026
Microsoft SharePoint Server Subscription Edition	KB5002833	Feb 10, 2026
Microsoft Word 2016 (32-bit edition)	KB5002839	Feb 10, 2026
Microsoft Word 2016 (64-bit edition)	KB5002839	Feb 10, 2026

Details

Published
February 10, 2026
Weakness
Deserialization of Untrusted Data
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21511

For tools and AI agents

This page as data: JSON · Markdown

Link to this page

If this page saved you time, a link to it in your ticket, advisory or write-up helps others find it.

HTML

<a href="https://patchblox.com/security/cve/CVE-2026-21511">CVE-2026-21511 on Patchblox Patch Radar</a>

Reusing the data? How to credit Patch Radar.

Is this on your machines?

Patchblox finds every install below the fixed version on Windows, macOS and Linux, and updates them through your release rings.

Get a demo

Patch Radar data is free to use with attribution. Terms and how to credit it.

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.