CVE-2025-1391 is an improper access control vulnerability identified in Keycloak version 26.0.0, specifically within its organization feature. The vulnerability arises from the way Keycloak assigns organizations to users based on matching their username or email against an organization’s domain pattern at the mapper level. Due to flawed logic, a user whose username or email matches the domain pattern of an organization can be incorrectly assigned to that organization. This misassignment is reflected in the tokens issued by Keycloak, which include claims indicating organizational membership. Applications that rely solely on these token claims for authorization decisions may incorrectly grant access or privileges to users who are not legitimate members of the organization. The vulnerability does not require user interaction and can be exploited remotely by an attacker with low privileges (PR:L), making it relatively easy to exploit in environments where Keycloak is deployed. The CVSS score of 5.4 (medium severity) reflects limited impact on confidentiality and integrity, with no impact on availability. There are no known exploits in the wild at the time of publication, but the risk remains significant for organizations that trust organization claims for access control. The issue stems from improper access control at the token mapper level, which is a critical component in identity federation and authorization workflows. Without additional verification, this flaw can lead to privilege escalation or unauthorized access within applications integrated with Keycloak. The vulnerability was published on February 17, 2025, and no official patches or fixes were linked in the provided data, indicating the need for organizations to monitor vendor advisories closely.

For European organizations, the impact of CVE-2025-1391 can be substantial, especially for those that use Keycloak as their identity and access management (IAM) solution. Misassignment of organizational membership in tokens can lead to unauthorized access to sensitive resources, data leakage, and potential privilege escalation within enterprise applications. This can undermine confidentiality and integrity of data and systems. Organizations in sectors such as finance, healthcare, government, and critical infrastructure that rely on Keycloak for fine-grained access control are at higher risk. The flaw could be exploited to bypass internal access restrictions, potentially exposing sensitive personal data protected under GDPR, leading to regulatory and reputational consequences. Since the vulnerability requires only low privileges and no user interaction, attackers with limited access could leverage this flaw to escalate privileges or move laterally within networks. The lack of availability impact means service disruption is unlikely, but unauthorized access risks remain significant. European organizations with complex multi-tenant or multi-organization deployments are particularly vulnerable due to reliance on organization claims for authorization.

1. Apply official patches or updates from Keycloak as soon as they become available to address the vulnerability at the source. 2. Until patches are released, disable or restrict the use of the organization feature or the affected mapper functionality to prevent incorrect organization assignment. 3. Implement additional authorization checks within applications that do not rely solely on token claims for organization membership; verify membership against authoritative back-end systems or directories. 4. Conduct thorough audits of token claims and access logs to detect anomalous organization assignments or unauthorized access patterns. 5. Enforce strict validation of usernames and emails to prevent attackers from crafting identifiers that match organization domain patterns. 6. Use multi-factor authentication and role-based access controls to limit the impact of any unauthorized access. 7. Educate developers and administrators about the risks of relying solely on token claims for authorization decisions and encourage defense-in-depth strategies. 8. Monitor threat intelligence feeds and vendor advisories for updates on exploits or patches related to CVE-2025-1391.