Microsoft Office Security Feature Bypass Vulnerability
Microsoft Office contains a security feature bypass vulnerability in which reliance on untrusted inputs in a security decision in Microsoft Office could allow an unauthorized attacker to bypass a security feature locally. Some of the impacted product(s) could be end-of-life (EoL) and/or end-of-service (EoS). Users are advised to discontinue use and/or transition to a supported version.
- Vendor
- Microsoft
- Product
- Office
- CVSS
- 7.8
- EPSS (exploit probability)
- 70.8%
- Status
- kev
- CISA patch-by (BOD 22-01)
- Added to KEV
Is CVE-2026-21509 being exploited?
Yes. CISA added CVE-2026-21509 to its Known Exploited Vulnerabilities catalog on . CISA only lists a CVE when it has reliable evidence of exploitation in the wild. It is also listed in CIRCL's KEV catalog.
FIRST's EPSS model puts the probability of exploitation activity in the next 30 days at 70.8% (scored November 9, 2026).
- CISA KEV[ LISTED ]
- ENISA EUVD (exploited)[ — ]
- CIRCL KEV[ LISTED ]
Catalog snapshot 2026-11-13. Full cross-catalog view: /kev-comparison
CVE-2026-21509 timeline
- Added to CIRCL KEVsame day as NVD
- Added to CISA KEVsame day as NVD
- Published to NVD
Every event links to its source. Catalog dates are each catalog's own; day offsets count from NVD publication. Data: JSON
What to do
CISA required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
US federal civilian agencies must remediate by (21 days after listing) under BOD 22-01. Everyone else: that deadline is a sensible upper bound, not a target. Vendor guidance and the NVD record are linked under Source above.
Other Microsoft Office CVEs we track
| CVE / Vulnerability | Severity | CVSS | EPSS | Added to KEV |
|---|---|---|---|---|
| CVE-2026-124194 Microsoft Office Outlook Missing User Interaction for Potentially Unsafe Action Vulnerability | [ MEDIUM ] | 6.5 | 1.6% | |
| CVE-2009-0238 Microsoft Office Remote Code Execution | [ HIGH ] | 8.8 | 42.9% | |
| CVE-2026-21514 Microsoft Office Word Reliance on Untrusted Inputs in a Security Decision Vulnerability | [ HIGH ] | 7.8 | 1.6% | |
| CVE-2009-0556 Microsoft Office PowerPoint Code Injection Vulnerability | [ HIGH ] | 8.8 | 67.3% | |
| CVE-2007-0671 Microsoft Office Excel Remote Code Execution Vulnerability | [ HIGH ] | 8.8 | 44.1% | |
| CVE-2023-23397 Microsoft Office Outlook Privilege Escalation Vulnerability | [ CRITICAL ] | 9.8 | 97.2% | |
| CVE-2023-21715 Microsoft Office Publisher Security Feature Bypass Vulnerability | [ HIGH ] | 7.3 | 12.0% | |
| CVE-2013-1331 Microsoft Office Buffer Overflow Vulnerability | [ HIGH ] | 7.8 | 79.8% |