Out-of-bounds read in Microsoft Office for macOS and Microsoft Office - CVE-2026-55139

Detailed vulnerability description

The vulnerability allows a remote attacker to disclose sensitive information.

The vulnerability exists due to out-of-bounds read in Microsoft Office for macOS when parsing a crafted Office file. A remote attacker can send a specially crafted file to the victim and convince them to open it to disclose sensitive information.

User interaction is required to open a crafted Office file, and the Preview Pane is not an attack vector.

How to mitigate CVE-2026-55139

Sources

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2026-55139
• https://www.microsoft.com/en-us/microsoft-365/mac/microsoft-365-for-mac?msockid=35f9adb0e74b61392038b90de6fe608c