Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check
cve-program · CVE-2026-18209
PublishedA 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.
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cve-program · CVE-2026-18209
PublishedKeycloak-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 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 published
- 31 Jul 2026 07:08:31 UTC
- Source modified
- 16 Sep 2026 18:36:58 UTC
- Saved here
- 23 Oct 2026 15:48:27 UTC
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CVSS 3.1 · 3.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N