A flaw was found in the SAML HTTP-Redirect binding implementation of Keycloak. The issue occurs because the server processes percent-encoded parameter names (like %53AMLResponse) while the signature verification logic only checks literal parameter names. An attacker can use this discrepancy to provide a crafted, unsigned SAML message that the server processes instead of a legitimately signed one, leading to full account takeover of federated users.
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
--- CME Mitigation Guidance (2026-11-06) ---
Disclaimer: The following mitigation solutions are provided as a courtesy, pending the application of an official patch. This content was generated utilizing AI tools in conjunction with data from https://cmetaxonomy.org. Customers are advised to independently evaluate and test these temporary mitigations within their own infrastructure.
The highest-value action is to align query parameter parsing between signature verification and request processing in Keycloak's SAML HTTP-Redirect binding so percent-encoded parameter names cannot evade signature checks: upgrade to the fixed Rhbk/Keycloak Rhel/Keycloak Services builds, which eliminates the parsing discrepancy between raw query parameter signature verification and decoded parameter processing in the SAML redirect binding, closing crafted HTTP GET request containing a percent-encoded unsigned SAML parameter placed before a legitimately signed parameter. Until patched, this is a concern on Keycloak instances configured to use SAML HTTP-Redirect binding for federated identity, so Audit and restrict account registration on external Identity Providers to prevent attackers from capturing legitimately signed redirect-binding messages. These controls limit blast radius and contain exploitation, but they do not fix the underlying SAML parameter parsing discrepancy signature bypass — apply the upstream patch to fully remediate.