Heap-based buffer overflow in Microsoft products - CVE-2026-78517

Vulnerability details

The vulnerability allows a remote attacker to execute arbitrary code.

The vulnerability exists due to a heap-based buffer overflow in Microsoft Office Word when handling a malicious Office file. A remote attacker can send a malicious Office file and convince a user to open it to execute arbitrary code.

The Preview Pane is not an attack vector.

Affected software

How to mitigate CVE-2026-78517

External References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2026-78517
• https://docs.microsoft.com/en-us/officeupdates/microsoft365-apps-security-updates

Related Security Bulletins

• Multiple vulnerabilities in Microsoft Office