CVE-2026-18209

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

• CWE-1288

• https://access.redhat.com/errata/RHSA-2026:68277
• https://access.redhat.com/errata/RHSA-2026:68278
• https://access.redhat.com/security/cve/CVE-2026-18209Vendor Advisory
• https://bugzilla.redhat.com/show_bug.cgi?id=2508305Issue Tracking, Vendor Advisory

Published

Jul 31, 2026

Last Modified

Sep 16, 2026

Status

Modified

• How Strix found a critical auth bypass in etcdStrix autonomously discovered a critical authentication bypass in etcd, later designated CVE-2026-33413.
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