CVE-2026-21509: listed in the CISA KEV catalog

CVE-2026-21509 · CVSS 7.8 HIGH · EPSS 72% · KEV 2026-01-26

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

Is CVE-2026-21509 exploited?

• Listed in the CISA KEV catalog on 2026-01-26.
• Federal remediation due 2026-02-16.
• Past that date by 180 days.
• EPSS puts exploitation in the next 30 days at 72%.
• Public exploit code: none found in monitored sources.

Which products and versions are affected?

No affected package list recorded here yet.

Is there a patch?

No patch identifier recorded here yet.

What PlainSec published about CVE-2026-21509

• APT28 Expands Supply-Chain Attacks Using Fresh Office Zero-Days (2026-04-09)
• APT28 Exploits CVE-2026-21509; Notepad++, OpenClaw, Chrome Targeted (2026-03-03)

Primary sources

• NVD record
• CISA KEV catalog

What this record does not say

• No affected package data.
• No patch identifier.

KEV and EPSS are re-checked daily. Record last updated 2026-08-11.