CVE-2026-18209
Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check
- Published
- Updated
- Reserved
- Assigned by
- redhat
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| redhatCNA (assigner) | 3.1 | Low3.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N |
| NVDNVD · Modified | 3.1 | Medium4.7 | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N |
- EPSS (exploitation in 30 days)
- 0.41% · top 65% of all CVEs (7 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Low 3.4.
Weakness
Affected products
Red Hat · Red Hat build of Keycloak 26.6
- unaffected 26.6.7-3 – < *
Red Hat · Red Hat build of Keycloak 26.6
- unaffected 26.6-20 – < *
Red Hat · Red Hat build of Keycloak 26.6
- unaffected 26.6-20 – < *
Red Hat · Red Hat build of Keycloak 26.6.7
All versions: unaffected
Red Hat · Red Hat build of Keycloak 26.6.7
All versions: unaffected
Red Hat · Red Hat build of Keycloak 26.6.7
All versions: unaffected
All versions: unaffected
Red Hat · Red Hat JBoss Enterprise Application Platform Expansion Pack
All versions: unaffected
Red Hat · Red Hat Single Sign-On 7
All versions: unaffected
What to do
Workaround: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
References (4)
- RHSA-2026:68277 (opens in a new tab)vendor-advisoryx_refsource_REDHAT
- RHSA-2026:68278 (opens in a new tab)vendor-advisoryx_refsource_REDHAT
- https://access.redhat.com/security/cve/CVE-2026-18209 (opens in a new tab)vdb-entryx_refsource_REDHAT
- RHBZ#2508305 (opens in a new tab)issue-trackingx_refsource_REDHAT
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-18209)Record last updated .