Bug 2535814 (CVE-2026-92855)

Summary: CVE-2026-92855 keycloak-services: keycloak-services: SAML broker accepts holder-of-key assertions without proof of key possession
Product: [Other] Security Response Reporter: Abhishek Raj <abhraj>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: aschwart, aszczucz, boliveir, drichtar, mposolda, pjindal, rmartinc, security-response-team, ssilvert, sthorger, vmuzikar
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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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.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Deadline: 2026-12-15   

Description Abhishek Raj 2026-09-17 04:57:34 UTC 
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.