CVE-2026-18209
LOWDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 9% of all known CVEs.
References
Related Vulnerabilities
Other CWE-1288 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2026-31431 | Medium | 5.5 | 100% | KEV | Fix |
| CVE-2023-6245 | High | 7.5 | 1.2% | - | Fix |
| CVE-2022-39353 | Critical | 9.4 | 1.2% | - | Fix |
| CVE-2021-41531 | High | 7.5 | 0.9% | - | Fix |
| CVE-2023-1620 | Medium | 4.9 | 0.9% | - | Fix |
| CVE-2024-25951 | High | 8.0 | 0.8% | - | Fix |
Common questions
How do I fix CVE-2026-18209?
No published fix for CVE-2026-18209 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-18209 being actively exploited?
Not that we know of. CVE-2026-18209 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.19% is the estimated probability that it will be exploited in the next 30 days. That is higher than 9% of all scored CVEs.
How severe is CVE-2026-18209?
CVE-2026-18209 has a CVSS v3 base score of 3.4, rated low. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-07.