Red Hat Keycloak keycloak-services session fixiation

Summaryinfo

A vulnerability, which was classified as problematic, was found in Red Hat Keycloak. Affected by this vulnerability is an unknown functionality of the component keycloak-services. The manipulation results in session fixiation. This vulnerability is cataloged as CVE-2026-18209. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Red Hat Keycloak (affected version not known). It has been classified as problematic. Affected is some unknown functionality of the component keycloak-services. The manipulation with an unknown input leads to a session fixiation vulnerability. CWE is classifying the issue as CWE-384. Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at access.redhat.com. This vulnerability is traded as CVE-2026-18209 since 07/29/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Additional levels of successful authentication are needed for exploitation. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $5k-$25k (estimation calculated on 07/31/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• Red Hat

Name

• Keycloak

License

• open-source

Website

• Vendor: https://www.redhat.com/

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Once again VulDB remains the best source for vulnerability data.

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