Use of uninitialized resource in Microsoft products - CVE-2026-55949
Published: July 17, 2026
Vulnerability identifier: #VU138249
CSH Severity: High
CVSS v4: 8.4 [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]
CVE-ID: CVE-2026-55949
CWE-ID: CWE-908
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to execute arbitrary code.
The vulnerability exists due to use of uninitialized resource in Microsoft Office Excel when parsing a crafted Office file. A remote attacker can send a specially crafted file and convince the victim 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.
Affected software
Microsoft Office for macOS
Microsoft Excel
Office Online Server
Microsoft Excel
Office Online Server
How to mitigate CVE-2026-55949
Install security update from vendor's website.
Microsoft Office for macOS - update to 16.111.26071215
Microsoft Excel - update to 16.0.5561.1001
Office Online Server - update to 16.0.10417.20175
Microsoft Excel - update to 16.0.5561.1001
Office Online Server - update to 16.0.10417.20175