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Vulnerability record · CVE-2026-18209 · published 31 July 2026

CVE-2026-18209: Redhat build of keycloak vulnerability

Redhat · Build Of Keycloak

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.

4.7 CVSS 3.1 Medium EPSS 0.41% · top 67.3% CWE-1288 · CWE-1288
4.7CVSS 3.1 base score
0.41%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
16 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

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

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-18209), CISA KEV, FIRST EPSS (scores of 2026-09-30). This page is refreshed as NVD updates the record.