CVE-2025-27478 is a heap-based buffer overflow vulnerability identified in the Windows Local Security Authority (LSA) component of Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The LSA is a critical security subsystem responsible for enforcing security policies, managing user authentication, and handling sensitive security tokens. This vulnerability arises due to improper handling of memory buffers on the heap, which can be exploited by an authorized local attacker to overwrite adjacent memory regions. Exploitation of this flaw allows the attacker to elevate their privileges on the affected system, potentially gaining SYSTEM-level access. The vulnerability requires local access with some privileges (low privileges) but does not require user interaction. The CVSS v3.1 base score is 7.0, indicating a high severity level. The attack vector is local (AV:L), with high attack complexity (AC:H), requiring privileges (PR:L), and no user interaction (UI:N). The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), meaning a successful exploit could fully compromise the system. No known exploits are currently reported in the wild, and no official patches have been linked yet. Given the nature of the vulnerability, exploitation could lead to complete system compromise, allowing attackers to bypass security controls, install persistent malware, or access sensitive data. The vulnerability is specific to Windows 10 Version 1809, which is an older version of Windows 10, but still in use in some environments.

For European organizations, this vulnerability poses a significant risk, especially in environments where Windows 10 Version 1809 is still deployed. The ability for a local attacker to escalate privileges could lead to insider threats or lateral movement by attackers who have gained limited access through other means. Critical infrastructure, government agencies, financial institutions, and enterprises relying on legacy Windows 10 systems could face severe consequences, including data breaches, disruption of services, and loss of sensitive information. The high impact on confidentiality, integrity, and availability means that successful exploitation could undermine trust in IT systems and lead to regulatory non-compliance under GDPR if personal data is compromised. Additionally, the lack of a patch at the time of disclosure increases the window of exposure. Organizations with remote desktop or terminal services exposing Windows 10 Version 1809 systems locally could be at increased risk if attackers gain initial footholds through phishing or other vectors.

1. Immediate mitigation should focus on reducing the attack surface by limiting local access to Windows 10 Version 1809 systems, especially for untrusted users. 2. Implement strict access controls and monitor for unusual privilege escalation attempts or suspicious LSA-related activity using endpoint detection and response (EDR) tools. 3. Where possible, upgrade affected systems to a newer, supported Windows version that does not contain this vulnerability. 4. Employ application whitelisting and restrict execution of unauthorized code to prevent exploitation payloads from running. 5. Use enhanced logging and auditing of security events related to LSA and privilege changes to detect early signs of exploitation. 6. Network segmentation should be enforced to isolate legacy systems and reduce lateral movement opportunities. 7. Prepare for patch deployment by testing updates once Microsoft releases an official fix, and prioritize patching affected systems promptly. 8. Educate users about the risks of local privilege escalation and enforce strong endpoint security policies to minimize insider threats.