CVE-2026-21509Microsoft Office Security Feature Bypass Vulnerability
Updated under an hour ago ()
Does this affect you?
It affects Microsoft 365 Apps for Enterprise and 7 other products. Add what you run to find out whether that includes you.
CISA lists it as known exploited since Jan 26, 2026; federal agencies had to remediate by Feb 16, 2026. Treat that date as your deadline.
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Free account, 1 product
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
- CVSS
- 7.8 HIGH (v3.1, CNA)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
- Weakness (CWE)
- CWE-807
- Known exploited
- Added to CISA KEV Jan 26, 2026; federal remediation due Feb 16, 2026Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- EPSS (exploitation in the next 30 days)
- 70.80% (percentile 99)
- Assigned by
- microsoft
- NVD analysis
- Analyzed
- Record last updated
- Jul 30, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
Microsoft Microsoft 365 Apps for Enterprise microsoft:365_apps_for_enterprise (from the name) | from 16.0.1 before https://aka.ms/OfficeSecurityReleases | CNA record |
Microsoft Microsoft Office 2016 microsoft:office_2016 (from the name) | from 16.0.0 before 16.0.5539.1001 | CNA record |
Microsoft Microsoft Office 2019 microsoft:office_2019 (from the name) | 19.0.0 builds before 16.0.10417.20095 | CNA record |
Microsoft Microsoft Office LTSC 2021 microsoft:office_ltsc_2021 (from the name) | from 16.0.1 before https://aka.ms/OfficeSecurityReleases | CNA record |
Microsoft Microsoft Office LTSC 2024 microsoft:office_ltsc_2024 (from the name) | from 16.0.0 before https://aka.ms/OfficeSecurityReleases | CNA record |
microsoft 365_apps microsoft:365_apps | all versions; all versions | NVD |
microsoft office microsoft:office | 2016; 2016; 2019; 2019 | NVD |
microsoft office_long_term_servicing_channel microsoft:office_long_term_servicing_channel | 2021; 2021; 2024; 2024 | NVD |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21509vendor-advisory, patch
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-detection-script-microsoft-office-security-feature-bypass-vulnerabilitythird-party-advisory
- https://www.vicarius.io/vsociety/posts/cve-2026-21509-mitigation-script-microsoft-office-security-feature-bypass-vulnerabilitymitigation, third-party-advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21509us-government-resource
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.