CVE-2026-55039 Microsoft Excel Remote Code Execution Vulnerability
An integer underflow in Microsoft Excel allows an attacker to execute arbitrary code locally, requiring a patch for all affected Office versions.
- Exploited in the wild
- Not known
- 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-2026-55039?
CVE-2026-55039 is a high-severity vulnerability in Microsoft 365 Apps, published on 14 Jul 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
Integer underflow (wrap or wraparound) in Microsoft Office Excel allows an unauthorized attacker to execute code locally.
Which versions are affected by CVE-2026-55039?
It affects 7 products.
Products include Microsoft 365 Apps, Microsoft Excel, Microsoft Microsoft 365, Microsoft Office 2019, Microsoft Office 2021, Microsoft Office 2024 and 1 more.
How do I fix CVE-2026-55039?
No fix has been published for CVE-2026-55039 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-55039 being exploited?
There is no known exploitation of CVE-2026-55039 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-h63h-p87q-mppp.