CVE-2026-21258

Published: Feb 10, 2026Modified: Jun 17, 2026

5.5

Vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

Exploitability: 1.8 / Impact: 3.6

Source: secure@microsoft.com (Secondary)

Description

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

Affected (13)

Products: Microsoft: 365 Apps, Excel, Office, Office Long Term Servicing Channel, Office Online Server

5 products

Office Long Term Servicing Channel

Office Online Server

Configuration A

13 vulnerable

Vulnerable Software	Affected Versions
Microsoft 365 Apps	All versions
Microsoft 365 Apps	All versions
Microsoft Excel	Version 2016
Microsoft Excel	Version 2016
Microsoft Office	Version 2019
Microsoft Office	Version 2019
Microsoft Office Long Term Servicing Channel	Version 2021
Microsoft Office Long Term Servicing Channel	Version 2021
Microsoft Office Long Term Servicing Channel	Version 2021
Microsoft Office Long Term Servicing Channel	Version 2024
Microsoft Office Long Term Servicing Channel	Version 2024
Microsoft Office Long Term Servicing Channel	Version 2024
Microsoft Office Online Server	Before 16.0.10417.20097

Related CWEs

Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer.

Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

References (1)

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21258

Source: secure@microsoft.com

Vendor Advisory

Timeline

No history available yet.