⚠ Actively exploited
Added to CISA KEV on 2026-01-26. Federal agencies required to patch by 2026-02-16. 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..

CVE-2026-21509

CWE-80716 documents12 sources
Severity
7.8HIGH
EPSS
7.5%
top 8.21%
CISA KEV
KEV
Added 2026-01-26
Due 2026-02-16
Exploit
No known exploits
Affected products
7
Microsoft Microsoft 365 Apps FOR EnterpriseMicrosoft Microsoft Office 2016Microsoft Microsoft Office 2019+4 more
Timeline
PublishedJan 26
KEV addedJan 26
KEV dueFeb 16
Latest updateMar 15
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.

Description

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

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HExploitability: 1.8 | Impact: 5.9

Affected Packages7 packages

▶CVEListV5microsoft/microsoft_office_201616.0.0 — 16.0.5539.1001
▶CVEListV5microsoft/microsoft_office_201919.0.0 — 16.0.10417.20095
▶CVEListV5microsoft/microsoft_office_ltsc_202116.0.1 — https://aka.ms/OfficeSecurityReleases
▶CVEListV5microsoft/microsoft_office_ltsc_202416.0.0 — https://aka.ms/OfficeSecurityReleases
▶NVDmicrosoft/office2016, 2019+1

🔴Vulnerability Details

3
GHSA
GHSA-ch84-h92g-mw93: Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally↗2026-01-26
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CVEList
Microsoft Office Security Feature Bypass Vulnerability↗2026-01-26
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VulnCheck
Microsoft Office Security Feature Bypass Vulnerability↗2026
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📋Vendor Advisories

2
CISA
Microsoft Office Security Feature Bypass Vulnerability↗2026-01-26
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Microsoft
Microsoft Office Security Feature Bypass Vulnerability↗2026-01-13
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🕵️Threat Intelligence

6
abuse.ch
BEARDSHELL - malicious payload (SHA-256 file hash)↗2026-03-15
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Bleepingcomputer
Russian hackers exploit recently patched Microsoft Office bug in attacks↗2026-02-02
▶
Talos
Microsoft releases update to address zero-day vulnerability in Microsoft Office↗2026-01-29
▶
Talos
Microsoft releases update to address zero-day vulnerability in Microsoft Office↗2026-01-29
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Wiz
CVE-2026-21509 Impact, Exploitability, and Mitigation Steps | Wiz↗
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