Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-07-28T12:55:48 keycloak-services: keycloak-services: secure-client-uris policy bypass via localhost-prefixed domains 4.2 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N CWE-20

A flaw was found in the secure-client-uris client policy executor within Keycloak core services. This component is responsible for enforcing security requirements on client configurations, such as requiring encrypted connections for redirect URIs. Due to an improper check that only looks at the start of a web address rather than properly verifying the host, an attacker can bypass these security restrictions by using a specially crafted domain name. This could allow an attacker to intercept sensitive authentication codes over unencrypted connections.

A flaw was found in the secure-client-uris client policy executor within Keycloak core services. This component is responsible for enforcing security requirements on client configurations, such as requiring encrypted connections for redirect URIs. Due to an improper check that only looks at the start of a web address rather than properly verifying the host, an attacker can bypass these security restrictions by using a specially crafted domain name. This could allow an attacker to intercept sensitive authentication codes over unencrypted connections.

The Red Hat Product Security team has assessed the severity of this vulnerability as Moderate, given that exploitation requires Dynamic Client Registration to be enabled and the attacker to control a specific localhost-prefixed domain. Successful exploitation allows an attacker to intercept authorization codes over cleartext HTTP by bypassing the secure-client-uris policy. The vulnerability's root cause is improper validation of the redirect URI host component in the secure-client-uris policy executor. Red Hat would like to thank Paul Bottinelli (Trail of Bits) for reporting this issue. Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability. Red Hat Build of Keycloak Affected keycloak-services Red Hat Build of Keycloak Affected rhbk-keycloak-rhel9/rhbk-keycloak-rhel9 Red Hat Build of Keycloak Affected rhbk-openshift-rhel9/rhbk-openshift-rhel9 Red Hat Data Grid 8 Not affected keycloak-services Red Hat JBoss Enterprise Application Platform Expansion Pack Not affected keycloak-services Red Hat Single Sign-On 7 Not affected keycloak-services https://www.cve.org/CVERecord?id=CVE-2026-18211 https://nvd.nist.gov/vuln/detail/CVE-2026-18211