CVE-2025-54895 is a high-severity vulnerability identified in Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The flaw arises from an integer overflow or wraparound condition within the SPNEGO (Simple and Protected GSSAPI Negotiation Mechanism) Extended Negotiation component. SPNEGO is a security protocol used for negotiating authentication mechanisms, commonly utilized in Windows environments for secure communications and authentication handshakes. The integer overflow occurs when a calculation involving integer values exceeds the maximum value the integer type can hold, causing it to wrap around to a lower value unexpectedly. This can lead to memory corruption or logic errors within the negotiation process. Exploiting this vulnerability requires local access and an authorized attacker with low privileges. By leveraging the integer overflow, the attacker can escalate their privileges on the affected system, potentially gaining higher-level access such as SYSTEM or administrator rights. The CVSS v3.1 score of 7.8 reflects the significant impact on confidentiality, integrity, and availability, with a complexity that is high due to the need for local access and existing privileges. The scope is changed, indicating that the vulnerability can affect resources beyond the initially compromised component. No known exploits are currently reported in the wild, and no patches have been linked yet, indicating that mitigation may rely on workarounds or awaiting official updates. The vulnerability is categorized under CWE-190 (Integer Overflow or Wraparound) and also relates to CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition), suggesting potential timing issues in the negotiation process. Overall, this vulnerability poses a serious risk to Windows 10 Version 1809 systems by enabling privilege escalation through a subtle flaw in authentication negotiation.

For European organizations, the impact of CVE-2025-54895 can be significant, especially for enterprises and government agencies still operating legacy Windows 10 Version 1809 systems. Privilege escalation vulnerabilities enable attackers who have already gained limited access (e.g., via phishing, insider threat, or other initial footholds) to elevate their privileges to administrative levels. This can lead to full system compromise, unauthorized access to sensitive data, disruption of critical services, and lateral movement within networks. Confidentiality, integrity, and availability of data and systems are all at risk. Organizations in sectors such as finance, healthcare, critical infrastructure, and public administration are particularly vulnerable due to the sensitive nature of their data and the criticality of their operations. The lack of known exploits in the wild currently provides a window for proactive mitigation, but the high severity score and potential for exploitation mean that organizations should prioritize addressing this vulnerability. Additionally, Windows 10 Version 1809 is an older release, so organizations that have not upgraded or patched systems may face increased risk. The vulnerability’s requirement for local access limits remote exploitation but does not eliminate risk, as attackers often gain local access through other means. Therefore, this vulnerability could facilitate more damaging attacks once initial access is achieved.

1. Upgrade and Patch: The most effective mitigation is to upgrade affected systems to a newer, supported Windows version or apply official patches once released by Microsoft. Monitor Microsoft security advisories closely for updates addressing CVE-2025-54895. 2. Restrict Local Access: Limit local user accounts and enforce strict access controls to reduce the number of users with low privileges who can log into critical systems. 3. Implement Application Whitelisting and Endpoint Protection: Use advanced endpoint detection and response (EDR) tools to monitor for suspicious privilege escalation attempts and block unauthorized processes. 4. Harden Authentication Mechanisms: Since the vulnerability is in SPNEGO Extended Negotiation, consider disabling or restricting the use of SPNEGO where feasible, or enforce stricter authentication policies and multi-factor authentication to reduce the risk of initial compromise. 5. Network Segmentation: Isolate legacy systems running Windows 10 Version 1809 from critical network segments to limit lateral movement opportunities. 6. Continuous Monitoring and Incident Response: Deploy monitoring solutions to detect unusual privilege escalation activities and prepare incident response plans to quickly contain and remediate any exploitation attempts. 7. User Training and Awareness: Educate users about the risks of local access compromise and enforce policies to prevent unauthorized physical or remote access to endpoints.