Zero-day vulnerability in Windows

Protection Mechanism Failure
CVE-2026-21513

Vulnerability details

Advisory: SB2026021058 - Remote code execution in Microsoft MSHTML Framework

Vulnerable component: Windows

CVE-ID: CVE-2026-21513

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

CWE-ID: CWE-693 - Protection Mechanism Failure

Description:

The vulnerability allows a remote attacker to compromise the affected system.

The vulnerability exists due to insufficient implementation of security measures within the ieframe.dll component when handling hyperlinks. An attacker can trick the the victim into clicking on a specially crafted link or on a shortcut (.lnk) file and execute arbitrary code on the system.

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

External links:

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513

https://www.akamai.com/blog/security-research/inside-the-fix-cve-2026-21513-mshtml-exploit-analysis

https://cert.gov.ua/article/6287250

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.