CVE-2026-40366 Microsoft Word Remote Code Execution Vulnerability
An attacker can execute arbitrary code locally by exploiting a type confusion vulnerability in Microsoft Word.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-40366?
CVE-2026-40366 is a high-severity use after free vulnerability in Microsoft 365 Apps, published on 12 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Access of resource using incompatible type ('type confusion') in Microsoft Office Word allows an unauthorized attacker to execute code locally.
Weakness: CWE-416
Which versions are affected by CVE-2026-40366?
It affects 4 products.
Products include Microsoft 365 Apps, Microsoft Office, Microsoft Office Long Term Servicing Channel, Microsoft Word.
How do I fix CVE-2026-40366?
No fix has been published for CVE-2026-40366 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-40366 being exploited?
There is no known exploitation of CVE-2026-40366 in the wild and no public exploit code.
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-gw2g-hq8h-6fvx.