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
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
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 14% 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-2022-39353 | Critical | 9.4 | 1.3% | - | Fix |
| CVE-2023-6245 | High | 7.5 | 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?
Published advisories record a fix for 2 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
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 0.23% is the estimated probability that it will be exploited in the next 30 days. That is higher than 14% 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.
What does CVE-2026-18209 affect?
Published advisories record a fix for rhbk/keycloak (Red Hat / RHEL), rhbk/keycloak (Rocky). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2026-18209
Markdown
[](https://tridentstack.com/cve/CVE-2026-18209)HTML
<a href="https://tridentstack.com/cve/CVE-2026-18209"><img src="https://tridentstack.com/cve/badge/CVE-2026-18209.svg" alt="CVE-2026-18209"></a>Check your Linux endpoints for this class of vulnerability
TridentStack Control continuously scans Linux endpoints for known vulnerabilities and deploys the fixes from the same console. 200 endpoints free forever, no credit card.
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 2026-09-16.