Red Hat Keycloak EUVD-2026-41556

Exploitation strictly requires that Fine-Grained Admin Permissions v2 (FGAP v2) is explicitly enabled on the target Keycloak realm - this is a non-default, opt-in feature and standard Keycloak deployments are not affected. The attacker must possess a delegated administrator account with at minimum client-management permissions within that realm; unauthenticated access or standard end-user accounts are insufficient. Limiting factors include the non-default FGAP v2 configuration gate, the requirement for a compromised or malicious delegated admin credential, and scope to the specific realms where FGAP v2 has been activated. Downstream application impact is further limited to relying parties that consume Keycloak-issued tokens without independently validating scope authorization.

The NVD CVSS 3.1 score of 5.4 (AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N) classifies this as medium severity, but the Scope:Unchanged assignment warrants scrutiny - the described impact explicitly crosses from Keycloak into downstream relying-party applications, which is a textbook scope-change scenario. A reassessed vector with S:C would elevate the base score. EPSS data was not supplied, and the vulnerability is absent from the CISA KEV catalog, meaning no confirmed in-the-wild exploitation or broad automated attack activity is evidenced. The realistic risk is meaningfully constrained by the non-default FGAP v2 prerequisite: deployments that have not intentionally enabled FGAP v2 are not exposed. For organizations that have enabled FGAP v2 and operate a delegated-administrator model, the risk is more significant because token manipulation in an IAM platform can produce cascading privilege escalation across all integrated applications without any of those applications being directly vulnerable. The combination of network accessibility, low attack complexity, and low privilege requirement (once FGAP v2 is active) makes this a priority for affected configurations despite the moderate base score.

An attacker who holds a delegated Keycloak administrator account - legitimately granted limited management rights over a specific client under FGAP v2 - calls the ClientResource admin API to enumerate and attach hidden client scopes that they are not authorized to view. The modified client now issues tokens to end-users that include those injected scopes; when those users present the tokens to downstream applications, the applications honor the unexpected scope claims and grant elevated access levels, effectively extending the attacker's permissions laterally across integrated services without ever directly compromising those services.