CVE-2025-55339 is an out-of-bounds read vulnerability classified under CWE-125 found in the Network Driver Interface Specification (NDIS) component of Microsoft Windows 11 Version 25H2 (build 10.0.26200.0). This vulnerability allows an attacker with authorized local access to read memory beyond the allocated buffer boundaries. The flaw arises due to improper bounds checking within the NDIS driver code, which handles network-related operations at a low system level. By exploiting this vulnerability, an attacker can potentially access sensitive kernel memory, leading to privilege escalation from a lower-privileged user to SYSTEM-level privileges. The CVSS v3.1 base score is 7.8, indicating high severity, with attack vector local (AV:L), low attack complexity (AC:L), requiring privileges (PR:L), and no user interaction (UI:N). The impact metrics indicate high confidentiality, integrity, and availability impacts (C:H/I:H/A:H). Although no known exploits are currently in the wild, the vulnerability's characteristics make it a significant risk for local privilege escalation attacks. The vulnerability was reserved in August 2025 and published in October 2025, with no patches publicly available at the time of reporting. The absence of patches necessitates immediate risk mitigation through access control and monitoring. The vulnerability's exploitation could allow attackers to bypass security controls, execute arbitrary code with elevated privileges, and compromise system stability and data confidentiality. Given the widespread deployment of Windows 11 25H2 in enterprise environments, this vulnerability poses a substantial threat to organizations relying on this platform.

For European organizations, the impact of CVE-2025-55339 is considerable due to the widespread use of Windows 11 Version 25H2 in corporate and government environments. Successful exploitation can lead to local privilege escalation, enabling attackers to gain SYSTEM-level access, which can be leveraged to deploy malware, exfiltrate sensitive data, or disrupt critical services. This is particularly concerning for sectors such as finance, healthcare, energy, and public administration, where confidentiality and availability are paramount. The vulnerability's ability to compromise integrity and availability means attackers could alter system configurations or cause denial of service, impacting business continuity. Since the attack requires local access, insider threats or compromised user accounts pose a significant risk. The lack of public exploits currently provides a window for proactive defense, but the high severity score underscores the urgency for mitigation. European organizations with remote or shared workstation environments are especially vulnerable if local access controls are weak. The potential for cascading effects in networked environments further amplifies the threat.

1. Apply official Microsoft patches immediately once they become available to address CVE-2025-55339. 2. Until patches are released, restrict local access to Windows 11 25H2 systems by enforcing strict user account control policies and limiting administrative privileges. 3. Implement robust endpoint detection and response (EDR) solutions to monitor for unusual local privilege escalation attempts or anomalous memory access patterns. 4. Harden network segmentation to reduce the risk of lateral movement from compromised local accounts. 5. Conduct regular audits of local user accounts and remove or disable unnecessary accounts with local access rights. 6. Employ application whitelisting and privilege management tools to limit execution of unauthorized code. 7. Educate users about the risks of local privilege escalation and enforce policies against installing unauthorized software or plugins. 8. Monitor system and security logs for signs of exploitation attempts, focusing on NDIS-related events and kernel memory access anomalies. 9. Prepare incident response plans specifically addressing local privilege escalation scenarios to enable rapid containment and remediation. 10. Coordinate with Microsoft support channels for early access to patches or workarounds if available.