This vulnerability in Red Hat Build of Keycloak involves improper input validation in the SAML HTTP-Redirect binding response handling. When a client uses a wildcard redirect URL, an attacker can inject malicious query parameters into the authentication request. Upon user authentication, Keycloak appends its legitimate SAML response to these attacker-controlled parameters without stripping or validating them. This parameter pollution can cause some service providers to process the attacker's data instead of the real login information, potentially resulting in login CSRF or session swapping attacks. Exploitation requires a specific client configuration and vulnerable downstream service providers. Red Hat rates the severity as Moderate but the CVSS score is 3.4 (low). No patch or effective mitigation is currently available according to Red Hat's advisory.

Successful exploitation can lead to login cross-site request forgery (CSRF) or session swapping on affected service providers, causing users to be logged into incorrect accounts. The vulnerability does not impact confidentiality or availability but has a low integrity impact. Exploitation requires a network attacker with no privileges and user interaction. The issue arises from improper handling of query strings in SAML HTTP-Redirect binding responses, leading to parameter pollution.

Red Hat currently does not provide a fix or mitigation that meets its criteria for ease of use, applicability, or stability. Users should be aware that mitigation options are limited or unavailable at this time. Monitoring Red Hat's advisory page for updates is recommended. No immediate action is mandated by Red Hat beyond awareness of the vulnerability and its conditions.