CVE-2026-21509
Microsoft Office Security Feature Bypass Vulnerability
- High 7.8
- Exploited: added to CISA KEV 26 Jan 2026
Description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
Key facts
- Published
- 26 Jan 2026
- Last changed
- 30 Jul 2026
- Assigned by
- microsoft
- KEV added
- 26 Jan 2026
- KEV fix due
- 16 Feb 2026
- EPSS
- 70.823% likely to be exploited in the next 30 days, higher than 99.409% of CVEs (scores for 15 Nov 2026)
- SSVC (CISA)
- Exploitation: active; Automatable: no; Technical impact: total
Severity scores
Each score is shown as its source gave it. They are not averaged or merged.
- 7.8CVSS 3.1, Highfrom the CNA (microsoft)
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
What 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.CISA KEV required action
Historical context and remediation
This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.
No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.
Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.
Affected products
| Vendor | Product | Versions |
|---|---|---|
| Microsoft | Microsoft 365 Apps for Enterprise |
|
| Microsoft | Microsoft Office 2016 |
|
| Microsoft | Microsoft Office 2019 |
|
| Microsoft | Microsoft Office LTSC 2021 |
|
| Microsoft | Microsoft Office LTSC 2024 |
|
Timeline
- 26 Jan 2026 Added to the CISA KEV catalogue
- 26 Jan 2026 Published