CVE-2026-21258 — Microsoft Excel Information Disclosure Vulnerability

Executive Summary

Improper input validation in Microsoft Office Excel allows an unauthorized attacker to disclose information locally.

Overview

5.5

CVSS MEDIUM

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Information Disclosure

Released Feb 10 2026

Last Updated Feb 10 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00596 — 0.43787 percentile

CVSS Vector

ATTACK VECTOR

Local

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

None

USER INTERACTION

Required

SCOPE

Unchanged

Temporal Score: 4.8

EPSS Score

0.00596

probability of exploitation in the next 30 days

0.43787 percentile - updated 2026-06-20

View on FIRST.org

Affected Products

13 affected products

Product	KB Article	Severity	Impact	Restart Required
Microsoft 365 Apps for Enterprise for 32-bit Systems	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft 365 Apps for Enterprise for 64-bit Systems	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft Excel 2016 (32-bit edition)	`5002837 (Security Update)`	Important	Information Disclosure	Maybe
Microsoft Excel 2016 (64-bit edition)	`5002837 (Security Update)`	Important	Information Disclosure	Maybe
Microsoft Office 2019 for 32-bit editions	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft Office 2019 for 64-bit editions	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft Office LTSC 2021 for 32-bit editions	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft Office LTSC 2021 for 64-bit editions	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft Office LTSC 2024 for 32-bit editions	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft Office LTSC 2024 for 64-bit editions	`Click to Run (Security Update)`	Important	Information Disclosure	No
Microsoft Office LTSC for Mac 2021	`Release Notes (Security Update)`	Important	Information Disclosure	Maybe
Microsoft Office LTSC for Mac 2024	`Release Notes (Security Update)`	Important	Information Disclosure	Maybe
Office Online Server	`5002835 (Security Update)`	Important	Information Disclosure	Maybe

Patches

4 patches

Article	Type	Restart
`Click to Run`	Security Update	No
`5002837`	Security Update	Maybe
`Release Notes`	Security Update	Maybe
`5002835`	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

Minjea Park

References

MSRC Advisory MITRE NVD