CVE-2025-12390 is a session fixation vulnerability identified in the Red Hat Build of Keycloak, an open-source identity and access management solution widely used for single sign-on and authentication services. The flaw arises because Keycloak sometimes reuses session identifiers and fails to properly clean up sessions during logout when browser cookies are missing. This improper session management can lead to a scenario where two different users sharing the same device and browser may inadvertently share session tokens, allowing one user to gain unauthorized access to another user's session. The vulnerability requires that both users operate on the same device/browser environment, and that the logout process does not clear session identifiers correctly due to missing cookies. The CVSS 3.1 vector indicates local attack vector (AV:L), high attack complexity (AC:H), low privileges required (PR:L), and user interaction required (UI:R). The impact on confidentiality and integrity is high because session tokens can be exposed and misused, but availability is not affected. No known exploits have been reported in the wild, and no patches have been linked yet, though Red Hat is expected to release fixes. This vulnerability highlights the importance of robust session management and cookie handling in authentication systems to prevent session fixation and unauthorized access.

For European organizations, especially those relying on Red Hat Build of Keycloak for identity and access management, this vulnerability poses a significant risk to user session confidentiality and integrity. Unauthorized access to user sessions could lead to data breaches, privilege escalation, and unauthorized actions performed under another user's identity. This is particularly critical in environments where devices are shared among multiple users, such as public terminals, call centers, or shared workstations. The risk is amplified in sectors handling sensitive personal data or critical infrastructure, including government agencies, financial institutions, and healthcare providers. Although exploitation requires local access and user interaction, the potential for insider threats or social engineering attacks exploiting this flaw is notable. The absence of proper session invalidation could undermine trust in authentication mechanisms and complicate compliance with GDPR and other data protection regulations.

Organizations should proactively monitor for updates and patches from Red Hat addressing this vulnerability and apply them promptly once available. In the interim, administrators should enforce strict session management policies, including ensuring that logout processes fully invalidate sessions and clear all session identifiers regardless of cookie presence. Implementing additional controls such as device fingerprinting or multi-factor authentication can reduce the risk of session misuse. Educate users about the risks of shared device usage and encourage practices such as closing browsers completely after logout. Where possible, restrict shared device usage or implement session timeout policies to minimize exposure. Conduct regular security audits and penetration testing focused on session management to detect similar issues. Finally, review and enhance cookie security settings, including setting the HttpOnly and Secure flags, to prevent session token leakage.