Use of uninitialized resource in Microsoft products - CVE-2026-55949
Published: July 17, 2026
Vulnerability identifier: #VU138249
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-2026-55949
CWE-ID: CWE-908
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 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.
How to mitigate CVE-2026-55949
Install security update from vendor's website.