CVE-2025-55339 is an out-of-bounds read vulnerability classified under CWE-125 affecting the Network Driver Interface Specification (NDIS) component in Microsoft Windows 11 Version 25H2 (build 10.0.26200.0). The vulnerability arises due to improper bounds checking in NDIS, allowing an attacker with authorized local access to read memory beyond intended boundaries. This memory disclosure can be leveraged to elevate privileges locally, potentially granting the attacker SYSTEM-level access. The vulnerability does not require user interaction and has a low attack complexity, but does require some level of local privileges, such as a standard user account. The CVSS v3.1 base score is 7.8, indicating high severity, with impacts rated high on confidentiality, integrity, and availability. No public exploits or proof-of-concept code have been reported yet, but the flaw’s nature suggests that exploitation could lead to complete system compromise. The vulnerability was reserved in August 2025 and published in October 2025, with no patches currently linked, indicating that organizations should monitor for updates from Microsoft. The attack vector is local, meaning remote exploitation is not feasible without prior access. This vulnerability is critical for environments where Windows 11 25H2 is deployed, especially in enterprise and critical infrastructure contexts where privilege escalation can lead to lateral movement and data breaches.

For European organizations, this vulnerability poses a significant risk due to the widespread adoption of Windows 11 in corporate and governmental environments. Successful exploitation could allow attackers to escalate privileges from a standard user to SYSTEM, enabling full control over affected machines. This can lead to unauthorized access to sensitive data, disruption of services, and potential deployment of further malware or ransomware. Critical sectors such as finance, healthcare, energy, and government agencies are particularly vulnerable because of the high value of their data and the potential for operational disruption. The local attack vector means that insider threats or attackers who have gained initial footholds through phishing or other means could leverage this vulnerability to deepen their access. Given the high confidentiality, integrity, and availability impacts, exploitation could result in severe data breaches, loss of trust, regulatory penalties under GDPR, and operational downtime.

Organizations should prioritize the following mitigations: 1) Monitor Microsoft’s security advisories closely and apply patches immediately once available to remediate the vulnerability. 2) Restrict local access to critical systems by enforcing least privilege principles and using strong authentication mechanisms. 3) Implement application whitelisting and endpoint detection and response (EDR) solutions to detect and block suspicious privilege escalation attempts. 4) Conduct regular audits of user privileges and remove unnecessary local accounts or rights. 5) Use network segmentation to limit lateral movement opportunities if an attacker gains local access. 6) Educate users about the risks of local exploitation and enforce strict controls on software installations and execution. 7) Employ advanced monitoring for anomalous behavior indicative of exploitation, such as unusual memory access patterns or privilege escalations. These steps go beyond generic patching by focusing on reducing the attack surface and improving detection capabilities.