FalehSec Exploited-vulnerability triage · joined from CISA KEV, NVD CVSS and EPSS

CVE-2026-21509

Microsoft · Office · Microsoft Office Security Feature Bypass Vulnerability

Verdict
Patch soon · actively exploited, not reachable unauthenticated from the internet, and in the top 1% of CVEs by near-term exploitation probability

Added to CISA KEV 2026-01-26 · exploited in the wild for 244 days

What an attacker can reach How likely Time What CISA says to do Sources All 545

What an attacker can reach

CVSS 7.8 HIGH. The score is a summary; these three components are the part that decides whether something scanning the internet can use it.

Attack vectorlocalrequires local access to the machine
Privileges requirednoneneeds no credentials at all
User interactionrequiredneeds a user to click, load or submit something first
Base vectorCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
WeaknessCWE-807

This describes the vulnerability. It says nothing about whether your systems run it.

How likely

EPSS puts the probability of exploitation in the next 30 days at 0.7287, which places it in the top 1% of all tracked CVEs. The percentile is the more useful half: 0.18 in absolute terms sounds low until you know most of the internet-facing software in the world scores under that.

EPSS probability0.7287
Percentile0.994 — top 1%

Time

Added to KEV2026-01-26
Days exploited244
Federal remediation duenot set
Ransomware useno known ransomware campaign use

What CISA says to do

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

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

Sources