Secuno
ENNL
Book demo

CVE-2026-21509

Microsoft Office Security Feature Bypass

7.8 HIGHActively exploited (CISA KEV)EPSS 70.8%
  1. Published26 Jan 2026
  2. Added to CISA KEV26 Jan 2026
  3. Remediation due16 Feb 2026
Actively exploited (CISA KEV)

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.

Added to KEV: 26 Jan 2026Federal remediation due: 16 Feb 2026

Description

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

CVSS 3.1 breakdown

Attack vectorLocal
Attack complexityLow
Privileges requiredNone
User interactionRequired
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Affected products

Microsoft 365 Appsall versions
Microsoft Office2016 · 2019
Microsoft Office Long Term Servicing Channel2021 · 2024

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

CVE-2026-946068.9
authentik is an open-source identity provider. Prior to 2026.2.7, 2026.5.7, and…
CVE-2026-844749.9
A flaw was found in Red Hat Ansible Automation Platform's automation- controller. The…
CVE-2026-857519.8
Mailu is a mail server distributed as a set of Docker images. From Mailu 2.0 until…
CVE-2026-811798.1
SysReptor is a fully customizable pentest reporting platform. Prior to 2026.58,…
CVE-2026-868639.8
pgAdmin 4's Webserver authentication source is intended to accept an identity asserted…
CVE-2026-874798.3
Insufficient policy enforcement in Extensions in Google Chrome prior to 153.0.8010.36…

Frequently asked

Is CVE-2026-21509 being actively exploited?

Yes. CVE-2026-21509 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, added 26 Jan 2026.

How severe is CVE-2026-21509?

CVE-2026-21509 has a CVSS 3.1 base score of 7.8, rated high. EPSS estimates a 70.8% probability of exploitation.

Which products are affected by CVE-2026-21509?

Affected products include Microsoft 365 Apps, Microsoft Office, Microsoft Office Long Term Servicing Channel.

How do I fix CVE-2026-21509?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-21509 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. Because it is on the CISA KEV list, Secuno flags any affected asset as top-priority automatically. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

See how prioritisation worksBook a demo

Running Microsoft 365?

Patching is one half. Scan your domain and check MFA, legacy authentication, admin roles and mail forwarding in two minutes, with a fix for every gap.

Run the free Microsoft 365 check

Get Patch this first every Monday

Five vulnerabilities that matter this week, ranked on real exploitation. Plain language, one email, no spam.

You can unsubscribe with one click from every issue. We handle your details as described in our privacy policy.

Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.