Reliance on Untrusted Inputs in a Security Decision in Microsoft Office - CVE-2026-21509
Published: January 26, 2026 / Updated: February 6, 2026
Vulnerability identifier: #VU122047
CSH Severity: Critical
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:A/U:Red
CVE-ID: CVE-2026-21509
CWE-ID: CWE-807
Exploitation vector: Remote access
Exploit availability:
The vulnerability is being exploited in the wild
Vendor: Microsoft
Affected software:
Microsoft Office
Microsoft Office
Detailed vulnerability description
The vulnerability allows a remote attacker to compromise the affected system.
The vulnerability exists due to improper insecure handling of OLE objects. A remote attacker can trick the victim into opening a specially crafted Office file and execute arbitrary code on the system.
Note, the vulnerability is being actively exploited in the wild.
How to mitigate CVE-2026-21509
Install updates from vendor's website.
Note, at the moment Microsoft Office 2016 and 2019 do not have a security update. Microsoft is working to release it.