Medium [CVE-2026-18570] Full-scope-disabled client policy validation bypass via omitted fullScopeAllowed

A flaw was found in the full-scope-disabled client-policy executor within the keycloak-services component. This component is responsible for enforcing security policies during client registration and configuration in Red Hat Build of Keycloak.

The issue occurs because the executor only validates the fullScopeAllowed field when it is explicitly provided in a request. By omitting this field, a delegated user can bypass the policy, resulting in a client created with full scope access.

This allows the client to obtain tokens with unauthorized role mappings. The Red Hat Product Security team has assessed the severity of this vulnerability as Moderate, given that exploitation requires the attacker to have delegated client creation privileges and the realm must have a specific policy configuration.

Successful exploitation allows an attacker to bypass client scope restrictions and obtain tokens with unauthorized permissions. The vulnerability's root cause is the failure of the policy executor to account for default server behavior when the fullScopeAllowed field is missing from a request.

Weakness: CWE-862. Affected Red Hat products: Red Hat build of Keycloak 26.6; Red Hat build of Keycloak 26.6.7.

Red Hat lists Red Hat Data Grid 8; Red Hat JBoss Enterprise Application Platform Expansion Pack; Red Hat Single Sign-On 7 as not affected.