Zero-day vulnerability in Windows Defender

Input validation error
CVE-2026-45498

Vulnerability details

Advisory: SB2026052119 - Denial of service in Microsoft Defender

Vulnerable component: Windows Defender

CVE-ID: CVE-2026-45498

CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L/E:H/RL:O/RC:C

CWE-ID: CWE-20 - Improper input validation

Description:

The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.

The vulnerability exists due to insufficient validation of user-supplied input. A remote attacker can pass a specially crafted file to the application and temporary disable antimalware protection. 

Note, the vulnerability is being actively exploited in the wild. 

External links:

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45498

About zero-day vulnerabilities

Zero-day vulnerability is an undisclosed vulnerability in software that hackers can exploit to compromise computer programs, gain unauthorized access to sensitive data, penetrate networks, etc. We consider vulnerability a zero-day when there is no solution provided from software vendor and the vulnerability is being actively exploited by malicious actors.

Zero-day candidate is a potential zero-day vulnerability in software which might have been used in targeted attacks, however there is no evidence to support this suggestion.