Access control vulnerability in Keycloak’s OIDC token introspection endpoint. The flaw is caused by not enforcing that the introspecting client is included in the token’s aud claim before returning introspection results. When a confidential attacker-controlled client obtains or intercepts an access token issued to a different audience, it can call the introspection endpoint and receive the full claim set, including claims intentionally omitted from lightweight access tokens. This can be exploited remotely by any confidential client in the realm with valid credentials. The vulnerability breaks the confidentiality model of lightweight tokens and allows unintended clients to recover sensitive attributes meant only for the legitimate resource server.