CVE-2026-21511

Microsoft Outlook Spoofing Vulnerability

State: Published
Severity: 7.5 High
Published: Feb 10, 2026
Updated: Aug 19, 2026
Reserved: Dec 30, 2025

Description

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

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C	microsoft

Weaknesses

CWE-502 Deserialization of Untrusted Data

Affected Products

Product	Versions
Microsoft 365 Apps for EnterpriseMicrosoft	16.0.1 to before https://aka.ms/OfficeSecurityReleasesAffected
Microsoft Office 2019Microsoft	19.0.0 to before https://aka.ms/OfficeSecurityReleasesAffected
Microsoft Office LTSC 2021Microsoft	16.0.1 to before https://aka.ms/OfficeSecurityReleasesAffected
Microsoft Office LTSC 2024Microsoft	16.0.0 to before https://aka.ms/OfficeSecurityReleasesAffected
Microsoft Office LTSC for Mac 2021Microsoft	16.0.1 to before 16.106.26020821Affected
Microsoft Office LTSC for Mac 2024Microsoft	16.0.0 to before 16.106.26020821Affected
Microsoft SharePoint Enterprise Server 2016Microsoft	16.0.0 to before 16.0.5539.1002Affected
Microsoft SharePoint Server 2019Microsoft	16.0.0 to before 16.0.10417.20097Affected
Microsoft SharePoint Server Subscription EditionMicrosoft	16.0.0 to before 16.0.19127.20518Affected
Microsoft Word 2016Microsoft	16.0.1 to before 16.0.5539.1002Affected

References

Microsoft Outlook Spoofing Vulnerabilityvendor-advisorypatch

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