CVE-2026-92855: Keycloak-services: keycloak-services: saml broker accepts holder-of-key assertions without proof of key possession
A flaw was found in the org.keycloak.broker.saml package of Keycloak. The SAML identity broker incorrectly handles signed assertions that contain only a holder-of-key SubjectConfirmation. When a bearer confirmation is absent, the broker skips the necessary subject-confirmation validation instead of enforcing proof of possession for the bound key. Exploitation requires that Keycloak is configured as a SAML broker with a trusted upstream provider that issues holder-of-key assertions. An attacker must obtain a valid signed assertion issued for a victim. No authentication or user interaction is required for the replay attack. Successful exploitation allows an attacker to bypass authentication mechanisms, impersonate any victim for whom they have a valid assertion, gain full access to the victim account and downstream applications, and issue new downstream assertions for the victim identity.
Other sources
A flaw was found in the SAML identity broker component of Keycloak, which is used to delegate authentication to external identity providers. The issue occurs because the broker fails to verify that a user actually possesses the private key associated with a holder-of-key assertion. An attacker who intercepts a victim signed assertion can replay it to gain unauthorized access and impersonate the victim without needing their private key.
— MITRE
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
The affected scenario is a Keycloak deployment configured as a SAML identity broker with a trusted upstream identity provider that issues holder-of-key assertions. The issue is relevant when those assertions lack a bearer SubjectConfirmation.
What does an attacker need to exploit the flaw?
An attacker needs a valid signed holder-of-key assertion issued for the victim by the trusted upstream provider. They do not need to authenticate to Keycloak or require user interaction to replay that assertion.
What can an attacker do after successful exploitation?
An attacker can bypass authentication and impersonate the victim associated with the assertion. This can provide full access to the victim account and downstream applications, including the ability to obtain new downstream assertions for that identity.