Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-05-19T10:50:49 keycloak: Keycloak: Access token disclosure and implicit flow bypass via forged client data 7.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N CWE-472

A flaw was found in Keycloak. A low-privilege user, with knowledge of user credentials and client ID, can bypass a security control intended to disable the implicit flow in OpenID Connect (OIDC) clients. By manipulating client data during a session restart, an attacker can obtain an access token that should not be available. This vulnerability can also lead to the exposure of these access tokens in server logs, proxy logs, and HTTP Referrer headers, resulting in sensitive information disclosure.

A flaw was found in Keycloak. A low-privilege user, with knowledge of user credentials and client ID, can bypass a security control intended to disable the implicit flow in OpenID Connect (OIDC) clients. By manipulating client data during a session restart, an attacker can obtain an access token that should not be available. This vulnerability can also lead to the exposure of these access tokens in server logs, proxy logs, and HTTP Referrer headers, resulting in sensitive information disclosure.

This High severity flaw in Keycloak allows a low-privilege user, with knowledge of user credentials and client ID, to bypass the `implicitFlowEnabled=false` setting. By forging client data during a session restart, an attacker can obtain an implicit access token, potentially exposing it in URL query strings if `response_mode=query` is also forged. This bypass undermines a critical security control intended to prevent implicit flow, leading to unauthorized access to sensitive tokens. Red Hat would like to thank Evan Hendra for reporting this issue. To mitigate this issue, restrict network access to the Keycloak authentication endpoint to trusted clients and networks. Implement firewall rules to control inbound connections to the Keycloak service ports, thereby reducing the attack surface and limiting who can initiate authentication flows and potentially exploit the implicit flow bypass. If the Keycloak service is reloaded or restarted, ensure these network restrictions remain in effect. Red Hat build of Keycloak 26.4 2026-05-20T00:00:00Z RHSA-2026:19597 rhbk/keycloak-operator-bundle:26.4.12-1 Red Hat build of Keycloak 26.4 2026-05-20T00:00:00Z RHSA-2026:19597 rhbk/keycloak-rhel9:26.4-17 Red Hat build of Keycloak 26.4 2026-05-20T00:00:00Z RHSA-2026:19597 rhbk/keycloak-rhel9-operator:26.4-17 Red Hat build of Keycloak 26.4.12 2026-05-20T00:00:00Z RHSA-2026:19596 rhbk/keycloak-rhel9-operator https://www.cve.org/CVERecord?id=CVE-2026-7571 https://nvd.nist.gov/vuln/detail/CVE-2026-7571