CVE-2026-21509
HighActively exploited (CISA KEV)
Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
SeverityHigh
CVSS7.8
Exploit probability—
Product
Microsoft Office
PublishedJan 26, 2026
First seenJan 26, 2026
Added to KEVJan 26, 2026
Weakness typeCWE-807CWE-807
How to fix
CISA required action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
CISA due date: Feb 16, 2026Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| microsoft office | 2016, 2019 | — |
| microsoft 365_apps | No range specified | — |
| microsoft office_long_term_servicing_channel | 2021, 2024 | — |
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