# CVE-2026-18209

## Summary

- **CVE ID:** CVE-2026-18209
- **Severity:** LOW
- **CVSS Score:** 3.4 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N)
- **CWE:** CWE-1288
- **Published:** Jul 31, 2026
- **Last Modified:** Jul 31, 2026

## 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.

## Affected Products

No affected products listed.

## References

- [CNA](https://access.redhat.com/security/cve/CVE-2026-18209)
- [CNA](https://bugzilla.redhat.com/show_bug.cgi?id=2508305)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.19%
- **EPSS Percentile:** 9.0

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._