CVE-2025-1391 is a medium-severity vulnerability affecting Keycloak version 26.0.0, specifically within its organization feature. The flaw arises from improper access control at the mapper level, where users can be incorrectly assigned to organizations if their username or email matches the organization's domain pattern. This misassignment leads to inaccurate claims embedded in authentication tokens. Applications that rely on these claims for authorization decisions may mistakenly grant users access or privileges intended only for members of those organizations. The vulnerability stems from insufficient validation of the relationship between user identity attributes and organizational membership, allowing potential privilege escalation or unauthorized access within systems that trust Keycloak's tokens for access control. The CVSS score of 5.4 reflects a network-exploitable issue with low attack complexity but requiring some privileges (PR:L) and no user interaction. The impact primarily affects confidentiality and integrity, as unauthorized users may gain access to sensitive resources or perform actions beyond their legitimate rights. There are no known exploits in the wild as of the publication date, and no patches or mitigation links were provided in the source information.

For European organizations, this vulnerability poses a risk of unauthorized access to internal applications and services that use Keycloak for identity and access management, especially those leveraging the organization claims for fine-grained authorization. Misassigned users could gain access to confidential data, internal tools, or privileged functions, potentially leading to data breaches, intellectual property theft, or disruption of business operations. Organizations in sectors with strict compliance requirements (e.g., finance, healthcare, government) may face regulatory and reputational consequences if unauthorized access occurs. The vulnerability could also facilitate lateral movement within networks if attackers exploit it to escalate privileges or access multiple organizational units. Given Keycloak's popularity as an open-source identity provider in Europe, the risk is non-trivial, particularly in enterprises and public sector entities that integrate it deeply into their authentication and authorization workflows.

To mitigate this vulnerability, European organizations should: 1) Immediately review and update Keycloak to a patched version once available, as no patch links were provided but vendors typically release fixes promptly. 2) Audit and validate the configuration of organization mappers to ensure that domain pattern matching is strict and cannot be bypassed by crafted usernames or emails. 3) Implement additional authorization checks at the application layer that do not solely rely on organization claims from tokens but verify membership through backend queries or trusted identity sources. 4) Monitor authentication logs for anomalous token claims or unexpected organization assignments. 5) Limit privileges granted based on organization claims until the vulnerability is remediated. 6) Educate developers and administrators about the risks of trusting token claims without validation. 7) Consider deploying compensating controls such as multi-factor authentication and network segmentation to reduce the impact of potential unauthorized access.