Integer underflow in Microsoft products - CVE-2026-55039
Published: July 17, 2026
Vulnerability identifier: #VU138207
CSH Severity: High
CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Amber
CVE-ID: CVE-2026-55039
CWE-ID: CWE-191
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Microsoft
Affected software:
Microsoft Office for macOS
Microsoft Excel
Office Online Server
Microsoft Office for macOS
Microsoft Excel
Office Online Server
Detailed vulnerability description
The vulnerability allows a remote attacker to execute arbitrary code.
The vulnerability exists due to integer underflow in Microsoft Office Excel when parsing a crafted Office file. A remote attacker can send a specially crafted file to a victim and convince them to open it to execute arbitrary code.
User interaction is required to open the crafted file, and the Preview Pane is not an attack vector.
How to mitigate CVE-2026-55039
Install security update from vendor's website.