CVE-2025-27727 is a high-severity local privilege escalation vulnerability affecting Microsoft Windows 10 Version 1809 (build 10.0.17763.0). The vulnerability arises from improper link resolution before file access in the Windows Installer component, categorized under CWE-59: Improper Link Resolution Before File Access ('Link Following'). This flaw allows an authorized attacker with limited privileges on the affected system to exploit the way Windows Installer resolves symbolic links or junction points before accessing files. By manipulating these links, an attacker can cause the system to access or modify files unintended by the original process, potentially overwriting or replacing critical system files or executing arbitrary code with elevated privileges. The vulnerability does not require user interaction but does require the attacker to have some level of local access (low privileges) to the system. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and privileges required. No known exploits are currently reported in the wild, and no official patches or mitigation links have been published yet. However, the vulnerability's nature suggests that once exploited, it could allow attackers to escalate privileges from a standard user to SYSTEM level, enabling full control over the affected machine. This is particularly concerning for environments where Windows 10 Version 1809 remains in use, despite being an older release, as it may still be present in legacy systems or specialized industrial environments.

For European organizations, the impact of CVE-2025-27727 could be significant, especially in sectors relying on legacy Windows 10 Version 1809 systems. Successful exploitation would allow attackers to elevate privileges locally, potentially bypassing security controls and gaining administrative access. This could lead to unauthorized access to sensitive data, disruption of critical services, and deployment of further malware or ransomware. Organizations in finance, healthcare, manufacturing, and government sectors are particularly at risk due to the sensitive nature of their data and the criticality of their operations. Additionally, the ability to escalate privileges without user interaction increases the risk of automated or stealthy attacks within internal networks. The vulnerability could also facilitate lateral movement within corporate networks, amplifying the potential damage. Given the lack of known exploits in the wild, the immediate risk is moderate, but the high severity score and potential impact warrant urgent attention, especially for organizations with compliance obligations under GDPR and other European data protection regulations.

To mitigate CVE-2025-27727 effectively, European organizations should: 1) Identify and inventory all systems running Windows 10 Version 1809 to assess exposure. 2) Apply any available security updates or patches from Microsoft as soon as they are released; monitor official Microsoft security advisories closely. 3) Implement strict local user privilege management by minimizing the number of users with local access and restricting permissions to only what is necessary. 4) Employ application whitelisting and endpoint protection solutions capable of detecting suspicious file system activities, such as unexpected symbolic link manipulations. 5) Use Group Policy settings to restrict the creation and resolution of symbolic links and junction points where feasible. 6) Monitor system logs and Windows Installer activity for anomalies indicative of link following exploitation attempts. 7) Consider upgrading affected systems to a more recent and supported Windows version to reduce exposure to legacy vulnerabilities. 8) Conduct regular security awareness training to ensure users understand the risks of local access and privilege escalation threats. These steps go beyond generic advice by focusing on controlling symbolic link usage, monitoring specific Windows Installer behaviors, and prioritizing legacy system upgrades.