CVE-2026-18209
Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check
At a glance
- Source
- NVD
- EPSS
- EPSS 0.41 % · percentile 35 ()
- State
- PUBLISHED
- Published
- Updated
- Assigner
- redhat
- NVD status
- Modified
Description
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.
Weaknesses (CWE)
References
Scores
| Version | Score | Vector | Scored by |
|---|---|---|---|
| CVSS 3.1 | LOW 3.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N | redhat |
| CVSS 3.1 | LOW 3.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N | NVD · secalert@redhat.com (Secondary) |
| CVSS 3.1 | MEDIUM 4.7 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N | NVD · nvd@nist.gov (Primary) |
European references
- ENISA EUVD · EUVD-2026-51487
- GCVE · GCVE-0-2026-18209
Affected configurations (NVD CPE)
cpe:2.3:a:redhat:build_of_keycloak:-:*:*:*:-:*:*:*
Affected products
Sources
| Source | Licence |
|---|---|
| CVE List (CVEProject cvelistV5) | CVE Program Terms of Use |
| EPSS (FIRST.org) | FIRST — attribution requested |
| ENISA EUVD | ENISA — reproduction authorised, source acknowledged |
| NVD (NIST) via fkie-cad/nvd-json-data-feeds | Public domain — this product uses data from the NVD API but is not endorsed or certified by the NVD |