CVE-2026-18209 — Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check
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 t…
Published: 2026-07-31 · CVSS: 3.4 · CVSS 3.1
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.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7