CVE-2026-21509

Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office…

Browse: All 2026 CVEs · All vendors

CVSS score
7.8 High
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CISA KEV
Yes — actively exploited (added 2026-01-26, remediation due 2026-02-16)
Weakness (CWE)
CWE-807
Published
2026-01-26
Last modified
2026-06-25
NVD status
Analyzed

Description

Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.

Affected products

Affected ranges per NVD CPE data; confirm exact versions in the vendor advisory.

Required action (CISA)

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Federal remediation deadline: 2026-02-16.

How to prioritize this

This vulnerability is on the CISA KEV list, meaning it is being actively exploited — treat it as urgent regardless of the raw CVSS number. Use the live CVE lookup for the latest NVD data, and the CVSS 3.1 calculator to model your own environmental score.

References

FAQ

Is CVE-2026-21509 actively exploited?

Yes. CISA added CVE-2026-21509 to its Known Exploited Vulnerabilities (KEV) catalog on 2026-01-26, with a federal remediation deadline of 2026-02-16. A KEV listing means real-world exploitation is confirmed, so patching this should be prioritized above many higher-CVSS bugs that aren't being exploited.

What is the CVSS score of CVE-2026-21509?

CVE-2026-21509 has a CVSS base score of 7.8 (High). Its vector string is CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

Related vulnerabilities

Data source: NVD & CISA KEV. Shown as-is; nothing added. Last generated from NVD data — re-check the live tool for updates.