Bug 2487006 (CVE-2026-11800)

Summary: CVE-2026-11800 org.keycloak:keycloak-services: Keycloak: Authentication bypass via JWT algorithm confusion
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: anujha, aschwart, asoldano, aszczucz, bbaranow, bmaxwell, boliveir, bstansbe, dlofthou, drichtar, istudens, ivassile, iweiss, mosmerov, mposolda, msvehla, nwallace, pesilva, pjindal, pmackay, rmartinc, rstancel, security-response-team, ssilvert, sthorger, thjenkin, vdosoudi, vmuzikar
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Keycloak. This JWT algorithm confusion vulnerability in the JWT Authorization Grant flow allows an attacker with valid client credentials to bypass signature verification. By forging an assertion, the attacker can create unauthorized access tokens. This enables the attacker to impersonate any federated user linked to the affected Identity Provider, leading to unauthorized access and potential privilege escalation.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Deadline: 2026-08-29   

Description OSIDB Bzimport 2026-06-09 14:09:56 UTC 
A JWT algorithm confusion vulnerability was found in Keycloak's JWT Authorization Grant flow . A flaw in the signature verification logic allows an attacker with valid client credentials to submit a forged assertion using alg=HS256 with the Identity Provider's public key bytes as the HMAC secret, bypassing asymmetric signature verification. This enables the attacker to mint access tokens and impersonate any federated user linked to the affected IdP. The vulnerability requires an IdP configured with jwtAuthorizationGrantEnabled=true, a hardcoded public key (useJwksUrl=false), and no pinned assertion signature algorithm (the default).