Microsoft · Office
CVE-2026-21509
Microsoft Office Security Feature Bypass Vulnerability
What it is
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
CISA: 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.
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.
Deadline for US federal agencies: February 16, 2026
More exploited flaws from Microsoft
| Added | Vulnerability | Product | Severity | Attack chance |
|---|---|---|---|---|
| Apr 14, 2026 | Remote Code Execution | Office | High 8.8 | 43% |
| Feb 10, 2026 | Word Reliance on Untrusted Inputs in a Security Decision | Office | High 7.8 | 1.6% |
| Jan 7, 2026 | PowerPoint Code Injection | Office | High 8.8 | 67% |
| Aug 12, 2025 | Excel Remote Code Execution | Office | High 8.8 | 43% |
| Mar 14, 2023 | Outlook Privilege Escalation | Office | Critical 9.8 | 97% |
| Feb 14, 2023 | Publisher Security Feature Bypass | Office | High 7.3 | 12% |
| Jun 8, 2022 | Object Record Corruption | Office | High 7.8 | 53% |
| Jun 8, 2022 | Buffer Overflow | Office | High 7.8 | 60% |
Sources: Known Exploited Vulnerabilities (CISA, public domain), CVE records (cve.org) and EPSS (FIRST). The chance of attacks is the EPSS estimate that someone will try to exploit the flaw in the next 30 days.