CVE-2026-21511 — Microsoft Outlook Spoofing Vulnerability

Executive Summary

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

Overview

7.5

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

More Likely

MS Exploit Likelihood

Category Spoofing

Released Feb 10 2026

Last Updated Feb 10 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.03635 — 0.88081 percentile

CVSS Vector

ATTACK VECTOR

Network

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

None

USER INTERACTION

None

SCOPE

Unchanged

Temporal Score: 6.5

EPSS Score

0.03635

probability of exploitation in the next 30 days

0.88081 percentile - updated 2026-06-20

View on FIRST.org

Affected Products

15 affected products

Product	KB Article	Severity	Impact	Restart Required
Microsoft 365 Apps for Enterprise for 32-bit Systems	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft 365 Apps for Enterprise for 64-bit Systems	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft Office 2019 for 32-bit editions	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft Office 2019 for 64-bit editions	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft Office LTSC 2021 for 32-bit editions	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft Office LTSC 2021 for 64-bit editions	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft Office LTSC 2024 for 32-bit editions	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft Office LTSC 2024 for 64-bit editions	`Click to Run (Security Update)`	Important	Spoofing	No
Microsoft Office LTSC for Mac 2021	`Release Notes (Security Update)`	Important	Spoofing	Maybe
Microsoft Office LTSC for Mac 2024	`Release Notes (Security Update)`	Important	Spoofing	Maybe
Microsoft SharePoint Enterprise Server 2016	`5002841 (Security Update) 5002840 (Security Update)`	Important	Spoofing	Maybe
Microsoft SharePoint Server 2019	`5002834 (Security Update) 5002836 (Security Update)`	Important	Spoofing	Maybe
Microsoft SharePoint Server Subscription Edition	`5002833 (Security Update)`	Important	Spoofing	Maybe
Microsoft Word 2016 (32-bit edition)	`5002839 (Security Update)`	Important	Spoofing	Maybe
Microsoft Word 2016 (64-bit edition)	`5002839 (Security Update)`	Important	Spoofing	Maybe

Patches

6 patches

Article	Type	Restart
`Click to Run`	Security Update	No
`Release Notes`	Security Update	Maybe
`5002841 (Security Update) 5002840`	Security Update	Maybe
`5002834 (Security Update) 5002836`	Security Update	Maybe
`5002833`	Security Update	Maybe
`5002839`	Security Update	Maybe

Known Exploits

No known exploits have been linked for this CVE yet. When available, exploit references will be sourced from public repositories and may be unverified, incomplete, or non-functional. Always review code carefully before use in any environment.

Acknowledgments

Office Product Group Security Team, Anonymous

References

MSRC Advisory MITRE NVD