CVE-2026-78518 Microsoft Office Excel Remote Code Execution Vulnerability
An out-of-bounds read in Microsoft Excel allows remote attackers to execute arbitrary code via a malicious file.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-78518?
CVE-2026-78518 is a high-severity memory corruption vulnerability in Microsoft 365 Apps, published on 8 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Out-of-bounds read in Microsoft Office Excel allows an unauthorized attacker to execute code over a network.
Which versions are affected by CVE-2026-78518?
It affects 7 products.
Products include Microsoft 365 Apps, Microsoft Excel, Microsoft Microsoft 365, Microsoft Office 2016, Microsoft Office 2019, Microsoft Office 2021 and 1 more.
How do I fix CVE-2026-78518?
No fix has been published for CVE-2026-78518 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-78518 being exploited?
There is no known exploitation of CVE-2026-78518 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-96qx-7xj2-vx4x.