CVE-2026-21245 is a heap-based buffer overflow vulnerability identified in the Windows Kernel component of Microsoft Windows 11 Version 24H2 (build 10.0.26100.0). This vulnerability is classified under CWE-122, indicating improper handling of memory buffers on the heap, which can lead to memory corruption. An attacker with authorized local access and limited privileges can exploit this flaw to execute arbitrary code with elevated privileges, effectively performing a local privilege escalation (LPE). The vulnerability does not require user interaction, which increases its risk profile. The CVSS v3.1 base score is 7.8, with attack vector Local (AV:L), low attack complexity (AC:L), privileges required are low (PR:L), no user interaction (UI:N), and impacts confidentiality, integrity, and availability at a high level (C:H/I:H/A:H). The scope remains unchanged (S:U), meaning the vulnerability affects only the vulnerable component and does not extend beyond it. Although no known exploits are currently reported in the wild, the nature of kernel-level heap overflows makes this a critical risk for privilege escalation attacks, potentially allowing attackers to bypass security controls and gain system-level access. The vulnerability was reserved in December 2025 and published in February 2026, indicating recent discovery and disclosure. No official patches or mitigations are listed yet, underscoring the need for vigilance and prompt patching once updates become available.

For European organizations, this vulnerability poses a significant threat due to the widespread use of Windows 11 in enterprise environments. Successful exploitation could allow attackers to escalate privileges from a low-privileged user account to SYSTEM or kernel-level privileges, enabling full control over affected systems. This can lead to unauthorized access to sensitive data, disruption of critical services, and the potential deployment of further malware or ransomware. The high impact on confidentiality, integrity, and availability makes it particularly dangerous for sectors such as finance, healthcare, government, and critical infrastructure operators. Additionally, the lack of required user interaction simplifies exploitation in scenarios where an attacker has local access, such as through compromised user accounts or insider threats. The vulnerability could also be leveraged in multi-stage attacks to bypass endpoint security controls and gain persistent footholds within networks. Given the strategic importance of IT infrastructure in Europe and the reliance on Windows 11, the potential for operational disruption and data breaches is substantial.

1. Monitor Microsoft security advisories closely and apply official patches immediately once released to remediate the vulnerability. 2. Restrict local access to systems running Windows 11 Version 24H2 by enforcing strict access controls and limiting administrative privileges. 3. Implement application whitelisting and endpoint detection and response (EDR) solutions to detect anomalous behavior indicative of privilege escalation attempts. 4. Conduct regular audits of user accounts and permissions to minimize the number of users with local access and reduce the attack surface. 5. Employ network segmentation to isolate critical systems and limit lateral movement in case of compromise. 6. Use virtualization-based security features available in Windows 11, such as Credential Guard and Hypervisor-protected Code Integrity (HVCI), to harden the kernel against exploitation. 7. Educate IT staff and users about the risks of local privilege escalation and the importance of reporting suspicious activity. 8. Prepare incident response plans that include scenarios involving kernel-level exploits to ensure rapid containment and recovery.