CVE-2026-21513 is a vulnerability classified under CWE-693 (Protection Mechanism Failure) affecting the MSHTML framework component in Microsoft Windows 10 Version 1607 (build 10.0.14393.0). MSHTML is a core rendering engine used by Internet Explorer and other Windows components to process HTML content. This vulnerability allows an attacker to bypass security features remotely over a network without requiring any privileges, but it does require user interaction, such as visiting a malicious webpage or opening a crafted document. The vulnerability results from improper enforcement of security controls within MSHTML, enabling unauthorized actions that compromise confidentiality, integrity, and availability of the affected system. The CVSS v3.1 base score is 8.8, reflecting high severity with network attack vector, low attack complexity, no privileges required, but user interaction needed. The scope is unchanged, meaning the vulnerability affects only the vulnerable component without extending to other system components. The impact includes potential remote code execution or elevation of privileges by bypassing security protections, which could lead to data theft, system manipulation, or denial of service. No public exploits or patches are currently available, but the vulnerability is officially published and recognized by Microsoft. Since Windows 10 Version 1607 is an older release, many organizations may still have legacy systems running this version, increasing the risk of exploitation if not mitigated. The lack of patches necessitates proactive measures such as upgrading to supported versions or applying workarounds to reduce attack surface.

For European organizations, the impact of CVE-2026-21513 is significant due to the potential for remote exploitation leading to unauthorized access and control over affected systems. Confidentiality breaches could expose sensitive corporate or personal data, while integrity compromises may allow attackers to alter critical files or system configurations. Availability could also be affected if attackers disrupt services or cause system crashes. Organizations relying on legacy Windows 10 Version 1607 systems, especially in sectors like finance, healthcare, and critical infrastructure, face heightened risks. The vulnerability's network attack vector and lack of privilege requirements make it easier for attackers to target exposed systems remotely, increasing the threat landscape. Additionally, the requirement for user interaction means phishing or social engineering campaigns could be used to trigger exploitation. The absence of known exploits currently provides a window for mitigation, but the high CVSS score and potential impact warrant urgent attention. Failure to address this vulnerability could lead to regulatory non-compliance under GDPR if personal data is compromised, resulting in legal and financial penalties.

1. Immediate inventory and identification of all systems running Windows 10 Version 1607 within the organization. 2. Prioritize upgrading affected systems to a supported and fully patched Windows version, such as Windows 10 Version 21H2 or later, to eliminate exposure. 3. Until upgrades are completed, implement network-level protections such as blocking access to untrusted websites and restricting inbound/outbound traffic to reduce exposure to malicious content exploiting MSHTML. 4. Employ endpoint protection solutions with heuristic and behavior-based detection capabilities to identify and block exploitation attempts targeting MSHTML. 5. Conduct user awareness training focused on recognizing phishing attempts and avoiding interaction with suspicious links or documents, as user interaction is required for exploitation. 6. Monitor security advisories from Microsoft for the release of official patches or workarounds and apply them promptly. 7. Utilize application whitelisting and sandboxing to limit the execution of untrusted code that could leverage this vulnerability. 8. Implement strict privilege management to minimize the impact if exploitation occurs, ensuring users operate with least privilege. 9. Regularly review and update incident response plans to include scenarios involving MSHTML exploitation.