CVE-2025-1391 is an improper access control vulnerability identified in Keycloak version 26.0.0, specifically affecting the organization feature's mapper logic. Keycloak uses mappers to assign claims to tokens based on user attributes. This vulnerability arises because the mapper incorrectly assigns an organization to a user if the user's username or email matches the organization's domain pattern. This logic flaw causes the token to contain claims indicating membership in an organization the user does not actually belong to. Applications relying on these claims for authorization decisions may mistakenly grant elevated privileges or access to unauthorized users. The vulnerability is exploitable remotely without user interaction and requires only low privileges (authenticated user). The CVSS 3.1 base score is 5.4 (medium severity), reflecting limited confidentiality and integrity impact but no availability impact. No patches or known exploits are currently reported, but the flaw poses a risk in environments where Keycloak is used as a central identity provider and authorization source. The issue highlights the importance of validating claims and not solely trusting token contents without additional verification.

The primary impact of CVE-2025-1391 is unauthorized access or privilege escalation within applications that rely on Keycloak's organization claims for authorization. Attackers can gain access to resources, data, or functions reserved for members of specific organizations by exploiting the flawed mapper logic. This can lead to data leakage, unauthorized actions, or compromise of organizational boundaries within multi-tenant or enterprise environments. Since Keycloak is widely used for identity and access management in cloud-native and enterprise applications, the vulnerability could affect numerous organizations globally. The impact is particularly significant for organizations with strict access controls based on organizational membership, such as financial institutions, healthcare providers, and large enterprises. However, the vulnerability does not affect system availability and requires an attacker to have at least low-level authenticated access, limiting the scope somewhat.

To mitigate CVE-2025-1391, organizations should first upgrade Keycloak to a version where this vulnerability is patched once available. Until a patch is released, administrators should review and tighten the configuration of organization mappers, avoiding reliance solely on username or email domain pattern matching for organization assignment. Implement additional authorization checks within applications that do not trust token claims blindly; for example, verify organization membership against a backend authoritative source. Employ strict monitoring and logging of authentication and authorization events to detect anomalous access patterns. Limit the exposure of Keycloak endpoints to trusted networks and enforce strong authentication policies to reduce the risk of low-privilege user exploitation. Finally, conduct thorough security assessments of identity and access management workflows to ensure no other similar logic flaws exist.