CVE-2026-21509

high

Description

Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509

https://www.cisa.gov/news-events/alerts/2026/01/26/cisa-adds-five-known-exploited-vulnerabilities-catalog

https://www.bleepingcomputer.com/news/microsoft/microsoft-patches-actively-exploited-office-zero-day-vulnerability/

https://securityaffairs.com/187349/hacking/emergency-microsoft-update-fixes-in-the-wild-office-zero-day.html

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509

Details

Source: Mitre, NVD

Published: 2026-01-26

Updated: 2026-01-27

Risk Information

CVSS v2

Base Score: 7.2

Vector: CVSS2#AV:L/AC:L/Au:N/C:C/I:C/A:C

Severity: High

CVSS v3

Base Score: 7.8

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

Severity: High

Vulnerability Watch

Tenable Research has classified this CVE under the following Vulnerability Watch classification, which includes active and historical (inactive) classifications. You can learn more about these classifications on our blog.

Vulnerability of Interest