CVE-2026-21250 is a vulnerability classified under CWE-822 (Untrusted Pointer Dereference) found in the HTTP.sys component of Microsoft Windows 11 Version 24H2 (build 10.0.26100.0). HTTP.sys is a kernel-mode driver responsible for handling HTTP requests, and improper handling of pointers can lead to dereferencing untrusted memory addresses. This flaw allows an attacker with authorized local access to manipulate pointer references, causing the system to execute arbitrary code with elevated privileges. The vulnerability does not require user interaction and has a low attack complexity, making it easier for attackers who already have some level of access to escalate privileges to SYSTEM level. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability. No public exploits are known yet, but the vulnerability's presence in a core Windows component makes it a critical concern. The flaw's exploitation could enable attackers to bypass security boundaries, install persistent malware, or disrupt system operations. The vulnerability was reserved in December 2025 and published in February 2026, with no patches currently available, emphasizing the need for vigilance and proactive mitigation.

For European organizations, the impact of CVE-2026-21250 could be severe. Many enterprises and government agencies rely heavily on Windows 11 for critical operations. Successful exploitation could lead to unauthorized privilege escalation, allowing attackers to gain SYSTEM-level access, which can compromise sensitive data, disrupt services, and facilitate further lateral movement within networks. This is particularly concerning for sectors such as finance, healthcare, energy, and public administration, where confidentiality and availability are paramount. The vulnerability's local attack vector means that attackers must first gain some form of local access, which could be achieved through phishing, insider threats, or exploiting other vulnerabilities. Once local access is obtained, this flaw could be used to fully compromise affected systems. The lack of known exploits currently provides a window for organizations to prepare, but the high severity score indicates that the threat should be treated urgently.

Since no official patches are currently available, European organizations should implement the following specific mitigations: 1) Restrict local access to Windows 11 systems, especially those running version 24H2, by enforcing strict access controls and using endpoint protection solutions to detect suspicious local activities. 2) Employ application whitelisting and privilege management to limit the ability of users and processes to execute unauthorized code or escalate privileges. 3) Monitor system logs and security events for unusual behavior indicative of privilege escalation attempts, focusing on HTTP.sys related processes. 4) Use network segmentation to isolate critical systems and reduce the risk of an attacker moving laterally after gaining local access. 5) Prepare for rapid deployment of Microsoft patches once released by establishing robust patch management processes. 6) Educate users and administrators about the risks of local access compromise and enforce strong authentication mechanisms to reduce initial access vectors. 7) Consider deploying host-based intrusion detection systems (HIDS) that can alert on kernel-level anomalies related to HTTP.sys.