Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
CVE-2026-18209
Red Hat Red Hat build of Keycloak 26.6 — Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check
AV AC PR UI S C I A CVSS EPSS %ile KEV
N L N R C N L N 4.7 .0041 32.8 —
AFFECTED
Product Versions Fixed
Red Hat build of Keycloak 26.6 unspecified 26.6.7-3
Red Hat build of Keycloak 26.6 unspecified 26.6-20
Red Hat build of Keycloak 26.6 unspecified 26.6-20
Red Hat build of Keycloak 26.6.7 unspecified —
Red Hat build of Keycloak 26.6.7 unspecified —
Red Hat build of Keycloak 26.6.7 unspecified —
Red Hat Data Grid 8 unspecified —
Red Hat JBoss Enterprise Application Platform Expansion Pack unspecified —
Red Hat Single Sign-On 7 unspecified —
TIMELINE
Jul 29 Reserved by redhat
Jul 31 Published (CNA: redhat)
Sep 16 PATCH SHIPPED — CVE-2026-18209 (Red Hat build of Keycloak 26.6). Fixed in Red Hat build of Keycloak 26.6 26.6.7-3.
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.
Lifecycle
Complete event history — 3 events, chronological
| Date | Event | Detail |
|---|
| July 29, 2026 | Reserved | Reserved by redhat |
| July 31, 2026 | Published | Published (CNA: redhat) |
| September 16, 2026 | PATCH SHIPPED | PATCH SHIPPED — CVE-2026-18209 (Red Hat build of Keycloak 26.6). Fixed in Red Hat build of Keycloak 26.6 26.6.7-3. |
Affected
Affected products and packages — 9 rows
| Vendor | Product / Package | Ecosystem | Version introduced | Fixed |
|---|
| Red Hat | Red Hat build of Keycloak 26.6 | — | — | 26.6.7-3 |
| Red Hat | Red Hat build of Keycloak 26.6 | — | — | 26.6-20 |
| Red Hat | Red Hat build of Keycloak 26.6 | — | — | 26.6-20 |
| Red Hat | Red Hat build of Keycloak 26.6.7 | — | — | — |
| Red Hat | Red Hat build of Keycloak 26.6.7 | — | — | — |
| Red Hat | Red Hat build of Keycloak 26.6.7 | — | — | — |
| Red Hat | Red Hat Data Grid 8 | — | — | — |
| Red Hat | Red Hat JBoss Enterprise Application Platform Expansion Pack | — | — | — |
| Red Hat | Red Hat Single Sign-On 7 | — | — | — |
About this page
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-18209 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.
