CVE-2025-54895 is a high-severity vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0) involving an integer overflow or wraparound issue within the SPNEGO (Simple and Protected GSSAPI Negotiation Mechanism) Extended Negotiation component. This vulnerability is classified under CWE-190, which pertains to integer overflow or wraparound errors. The flaw allows an authorized local attacker—meaning the attacker must have some level of access to the system—to exploit the integer overflow condition to elevate their privileges on the affected system. The vulnerability impacts confidentiality, integrity, and availability, as indicated by the CVSS vector (C:H/I:H/A:H), and has a CVSS v3.1 base score of 7.8, categorizing it as high severity. The attack complexity is high (AC:H), requiring the attacker to have low privileges (PR:L) but no user interaction (UI:N). The scope is changed (S:C), meaning the vulnerability can affect resources beyond the initially vulnerable component. The vulnerability does not currently have known exploits in the wild, and no patches have been linked yet, though the vulnerability was publicly disclosed on September 9, 2025. The integer overflow in SPNEGO Extended Negotiation could allow an attacker to manipulate negotiation data structures or buffers, potentially leading to memory corruption and privilege escalation. Given that SPNEGO is involved in authentication negotiation protocols, exploitation could undermine system security mechanisms, allowing attackers to gain elevated rights and perform unauthorized actions locally.

For European organizations, this vulnerability poses a significant risk, especially in environments where Windows 10 Version 1809 is still in use, such as legacy systems or industrial control systems that have not been updated. Privilege escalation vulnerabilities can lead to attackers gaining administrative control, enabling them to deploy malware, exfiltrate sensitive data, disrupt operations, or move laterally within networks. The compromise of confidentiality, integrity, and availability could affect critical sectors including finance, healthcare, government, and manufacturing. Since the vulnerability requires local access, insider threats or attackers who have gained initial footholds through other means could leverage this flaw to deepen their control. The lack of a patch at the time of disclosure increases the window of exposure. Additionally, the complexity of exploitation being high may limit widespread automated attacks, but targeted attacks against high-value European organizations remain a concern. The vulnerability's impact is amplified in environments with weak endpoint security or where Windows 10 1809 is prevalent due to delayed upgrades.

European organizations should prioritize the following mitigation steps: 1) Identify and inventory all systems running Windows 10 Version 1809 to assess exposure. 2) Apply any available security updates or patches from Microsoft immediately once released. In the absence of patches, consider temporary mitigations such as restricting local user privileges and enforcing strict access controls to limit who can log on locally. 3) Monitor systems for unusual local privilege escalation attempts, including anomalous SPNEGO negotiation traffic or suspicious process behavior. 4) Employ endpoint detection and response (EDR) tools capable of detecting exploitation attempts targeting privilege escalation vulnerabilities. 5) Where possible, upgrade affected systems to newer, supported Windows versions that do not contain this vulnerability. 6) Implement network segmentation to isolate critical assets and reduce the risk of lateral movement if a local compromise occurs. 7) Conduct user awareness and insider threat training to reduce the risk of authorized users exploiting this vulnerability. 8) Review and harden authentication and negotiation protocols related to SPNEGO to reduce attack surface.