Description

A flaw was found in the Dynamic Client Registration component of Keycloak, an open-source identity and access management solution. The issue occurs because the system does not properly restrict which claim names can be used when setting up new clients. An attacker with valid registration credentials could create a client that incorrectly maps standard user profile information to sensitive security roles, potentially allowing them to gain unauthorized privileges on external applications that trust Keycloak tokens.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.5",
  "pubDate": "2026-11-06T06:16:45.220Z",
  "pubdate": "2026-11-06T06:16:45.220Z",
  "executiveSummary": "A critical security flaw exists within the Dynamic Client Registration component of Keycloak, an open-source identity and access management platform. The vulnerability is classified as an improper input validation and access control issue, allowing an authenticated attacker with valid registration credentials to manipulate claim mappings during the client creation process.\nBy failing to restrict the configuration of claim names, the system permits the injection of unauthorized mappings. This allows an attacker to manipulate standard user profile attributes to correspond with sensitive security roles or claims. Consequently, tokens issued to such clients may inherit elevated privileges, leading to potential unauthorized access within external applications that rely on Keycloak as an identity provider.\nThe risk is significant for organizations utilizing Dynamic Client Registration in environments where clients are permitted to define their own token structures. Exploitation requires the attacker to possess valid registration credentials, which are typically granted to authorized users or service accounts. The impact involves a compromise of the integrity and confidentiality of the authentication process, potentially granting attackers administrative or escalated access to downstream services that trust the identity tokens generated by the compromised Keycloak instance.",
  "technicalDetails": "The vulnerability resides within the Dynamic Client Registration service of Keycloak, which facilitates the automated provisioning of OIDC/OAuth2 clients. The core issue is an insufficient validation mechanism concerning the client configuration payload. Specifically, the component fails to sanitize or enforce an allow-list for claim names during the registration process, enabling the injection of arbitrary mappings between user attributes and sensitive security tokens.\nThe exploitation flow begins with an attacker obtaining valid registration credentials for the target Keycloak instance. Using these credentials, the attacker invokes the Dynamic Client Registration endpoint to initiate the creation of a new client. Within the registration request payload, the attacker includes specifically crafted claim mapping configurations. By targeting sensitive claim names or roles that are normally reserved for administrative or internal use, the attacker forces the Keycloak server to include these mappings in the JWT (JSON Web Token) issuance process for the new client.\nUpon successful registration, any subsequent authentication flow using this malicious client results in the generation of access tokens containing the forged claims. Because Keycloak does not validate that the registered client is permitted to map specific internal attributes to token claims, the downstream applications—which verify the signature and claim set of the JWT—will inadvertently honor the escalated privileges dictated by the manipulated token payload.\nThis vulnerability effectively circumvents standard Role-Based Access Control (RBAC) enforced by Keycloak. Since the trust is established at the token validation layer by external services, the malicious mapping persists across the ecosystem. The exploit does not require complex infrastructure, only the ability to interact with the registration API using valid credentials. The post-exploitation impact is severe, as it enables lateral movement and privilege escalation across all external applications consuming tokens from the affected identity provider. The flaw highlights a failure in the trust boundary between client-provided configuration and server-side authorization enforcement, where user-supplied input is treated as trusted metadata during the client definition phase."
}