CVE-2026-18209Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check
Updated under an hour ago ()
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It affects Red Hat build of Keycloak 26.6 and 4 other products. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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
- 3.4 LOW (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N
- Weakness (CWE)
- CWE-1288
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- redhat
- NVD analysis
- Modified
- Record last updated
- Sep 16, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.