CVE-2026-21509 Microsoft Office Security Feature Bypass
An attacker can bypass security features in Microsoft Office by exploiting reliance on untrusted inputs, requiring local access.
- Exploited in the wild
- Since 26 Jan 2026
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-21509?
CVE-2026-21509 is a high-severity vulnerability in Microsoft 365 Apps, published on 26 Jan 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
Reliance on untrusted inputs in a security decision in Microsoft Office allows an unauthorized attacker to bypass a security feature locally.
Weakness: CWE-807
Which versions are affected by CVE-2026-21509?
It affects 3 products.
Products include Microsoft 365 Apps, Microsoft Office, Microsoft Office Long Term Servicing Channel.
How do I fix CVE-2026-21509?
No fix has been published for CVE-2026-21509 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 16 Feb 2026.
Is CVE-2026-21509 being exploited?
Yes. Attackers have exploited CVE-2026-21509 in the wild since at least 26 Jan 2026.
Public exploit code: 13 proofs of concept on GitHub.
Other vulnerabilities in Microsoft 365 Apps
- CVE-2024-21413 Microsoft Outlook Improper Input Validation
- CVE-2023-23397 Microsoft Office Outlook Privilege Escalation
- CVE-2024-38189 Microsoft Project Remote Code Execution Vulnerability
- CVE-2023-35311 Microsoft Outlook Security Feature Bypass
- CVE-2026-21514 Microsoft Office Word Reliance on Untrusted Inputs in a Security Decision
Sources
Also known as GHSA-ch84-h92g-mw93.