CVE-2026-21511

HIGH

Microsoft 365 Apps and Office - Spoofing via Untrusted Data Deserialization

Title source: llm
STIX 2.1

Description

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

References (1)

Core 1
Core References

Scores

CVSS v3 7.5
EPSS 0.0364
EPSS Percentile 88.1%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

CISA SSVC

Vulnrichment
Exploitation none
Automatable yes
Technical Impact partial

Details

CWE
CWE-502
Status published
Products (18)
microsoft/365_apps (2 CPE variants)
Microsoft/Microsoft 365 Apps for Enterprise 16.0.1 - https://aka.ms/OfficeSecurityReleases
Microsoft/Microsoft Office 2019 19.0.0 - https://aka.ms/OfficeSecurityReleases
Microsoft/Microsoft Office LTSC 2021 16.0.1 - https://aka.ms/OfficeSecurityReleases
Microsoft/Microsoft Office LTSC 2024 16.0.0 - https://aka.ms/OfficeSecurityReleases
Microsoft/Microsoft Office LTSC for Mac 2021 16.0.1 - 16.106.26020821
Microsoft/Microsoft Office LTSC for Mac 2024 16.0.0 - 16.106.26020821
Microsoft/Microsoft SharePoint Enterprise Server 2016 16.0.0 - 16.0.5539.1002
Microsoft/Microsoft SharePoint Server 2019 16.0.0 - 16.0.10417.20097
Microsoft/Microsoft SharePoint Server Subscription Edition 16.0.0 - 16.0.19127.20518
... and 8 more
Published Feb 10, 2026
Tracked Since Feb 18, 2026