CVE-2026-18217: Keycloak-services: keycloak-services: saml http-redirect binding response preserves query string leading to parameter pollution

Vulnerability summary

CVE-2026-18217 is a medium (CVSS 4.7) Improper Input Validation vulnerability in redhat build_of_keycloak. EPSS estimates a 0.33% chance of exploitation in the next 30 days, higher than 25.1% of scored vulnerabilities.

Timeline

1. 31-07-2026
   PublishedVulnerability first disclosed.
2. 31-07-2026
   Last modifiedVulnerability information updated.

Description

A flaw was found in the SAML protocol implementation of Keycloak, an open-source identity and access management solution. The issue occurs when Keycloak handles SAML authentication requests using the HTTP-Redirect binding. If a client is configured with a wildcard redirect URL, an attacker can craft a request that includes malicious parameters. When a user authenticates, Keycloak appends its legitimate response to the attacker's parameters. This can cause some service providers to process the attacker's data instead of the real login information, potentially leading to a user being logged into the wrong account.

• CWE-20Improper Input ValidationThe product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.